The course is an introduction to cybersecurity for technical and non-technical audiences alike. Students learn how to secure their accounts, data, systems, and software against today’s threats and how to recognize and evaluate tomorrow’s as well, both at home and at work. Students learn how to preserve their own privacy. Students learn to view cybersecurity not in absolute terms but relative, a function of risks and rewards (for an adversary) and costs and benefits (for them), and to recognize cybersecurity as a trade-off with usability itself. The course presents both high-level and low-level examples of threats, providing students with all they need to know technically to understand both. Assignments are inspired by real-world events.


David J. Malan

Head Teaching Fellow

Doug Lloyd


You are expected to

  • watch five lectures,
  • attend five live sections (one per lecture),
  • submit five quizzes,
  • submit five assignments,
  • submit one exam, and
  • submit a final project.


Final grades are determined using the following weights:

Assignments 50%
Quizzes 5%
Exam 20%
Final project 15%
Section attendance 10%

Many questions on the assignments in this course are out of 3 points. When you receive your feedback on these assignments, these scores translate as follows:

  • 3 is reserved for exceptional answers that demonstrate a full understanding of the material in a manner that exceeds the course’s expectations, which may sometimes involve external research. Please note that this does not necessarily mean a long answer; indeed, an overly long answer that introduces irrelevant information is not likely to receive a 3. Rather, a 3 is awarded to a thorough and well thought-out and prepared answer that focuses on the subject of the question being presented. Only a few 3s at most will be awarded per question.
  • 2 is awarded for a good to great answer that demonstrates understanding of the material in a manner consistent with the course’s expectations. Most correct answers will be graded a 2, and a score of 2 should be considered your benchmark for success.
  • 1 is awarded for a poor to fair answer that either demonstrates partial understanding of the material or otherwise contains an error that suggests a misunderstanding of a key detail.
  • 0 is given to answers that are incorrect, exceedingly brief, or blank.

Grades in this course should not be converted to percentages and assumed to be accurate, because they will not be. A 2 out of 3 on a question, as indicated above, is a “benchmark for success,” and not a 66.6% (D). The course does not have pre-determined cutoffs for final grades. Beyond what is stated here, the course does not provide further detail about grade conversions. The course does not offer mid-semester grade projections, as each element’s weight, above, can materially alter that projection. As is the case in any course with writing-based assignments, there is a degree of subjectivity in grading; however, the course heads will not ordinarily reverse scores or entertain regrade requests except in cases of clear, demonstrable error, such as in cases where the feedback left by the staff is so incongruous with the score received that the only explanation is human error. Grading is spot-checked by the course heads prior to release to students to ensure consistency.


  Released Topic
Lecture 0 2023-09-05T12:00:00-04:00 Securing Accounts
Lecture 1 2023-09-18T12:00:00-04:00 Securing Data
Lecture 2 2023-10-02T12:00:00-04:00 Securing Systems
Lecture 3 2023-10-23T12:00:00-04:00 Securing Software
Lecture 4 2023-11-06T12:00:00-05:00 Preserving Privacy


Quizzes are short assessments (for which completion, not necessarily correctness, is important) associated with each lecture that allow you to apply each week’s concepts before digging in deeper in section.

  Released Due
Quiz 0 2023-09-05T12:00:00-04:00 2023-09-07T23:59:00-04:00
Quiz 1 2023-09-18T12:00:00-04:00 2023-09-21T23:59:00-04:00
Quiz 2 2023-10-02T12:00:00-04:00 2023-10-05T23:59:00-04:00
Quiz 3 2023-10-23T12:00:00-04:00 2023-10-26T23:59:00-04:00
Quiz 4 2023-11-06T12:00:00-05:00 2023-11-09T23:59:00-05:00


Lectures are supplemented by 60 to 90-minute sections led by the teaching fellows. Sections are an opportunity to discuss the course’s material, ask questions, and explore related material. Students are required to attend, live and with webcam and audio enabled, one section per lecture unless granted an exception in writing by the course’s head teaching fellow within 48 hours after you have been emailed your section assignment. If circumstances change mid-semester, and you find yourself no longer able to attend sections when you previously were able to, contact the head teaching fellow.

Office Hours

Office hours are opportunities for guidance and feedback from the staff on assignments as well as for discussion of the course’s material more generally. Students are not required to attend these sessions if they do not feel they need to.


Assignments introduce or reinforce material via exercises, readings, questions, and/or videos.

  Released Due
Assignment 0 2023-09-05T12:00:00-04:00 2023-09-17T23:59:00-04:00
Assignment 1 2023-09-18T12:00:00-04:00 2023-10-01T23:59:00-04:00
Assignment 2 2023-10-02T12:00:00-04:00 2023-10-15T23:59:00-04:00
Assignment 3 2023-10-23T12:00:00-04:00 2023-11-05T23:59:00-05:00
Assignment 4 2023-11-06T12:00:00-05:00 2023-11-19T23:59:00-05:00


The (take-home) exam synthesizes and assesses mastery of the course’s material. Its format will not be unlike an assignment.

Released Due
2023-11-30T12:00:00-05:00 2023-12-10T23:59:00-05:00

Final Assessment

The final assessment is an opportunity to take lessons learned in the course and apply them at a higher level.

released due
2023-11-20T12:00:00-05:00 2023-12-15T23:59:00-05:00
  • The final project also has two intermediate milestones. This is the deadline for the third and final milestone.

Lateness Policy

You have a semester-long allowance of 72 hours (divided into 1-minute segments) to turn in assignments (not the exam, not quizzes, and not the final) late. This allowance should be used carefully (if at all!), but can otherwise be allocated in any manner of your choosing, which means that you may:

  • Use the full 72 hours on one assignment; or
  • Use a bit over 14 hours on each assignment; or
  • Use 9 hours and 22 minutes on one assignment, 30 hours and 11 minutes on another, 54 minutes on a third, etc.

Once the 72-hour allowance has been exhausted, then from that point on the course will begin to impose a 0.1% deduction to your grade for an assignment for each minute it is turned in late. Therefore, once your allowance is exhausted, for example:

  • Any work turned in 10 minutes late will earn 99% of the points it would have earned had it been turned in on time (a 1.0% deduction).
  • Any work turned in 60 minutes late will earn 94% of the points it would have earned had it been turned in on time (a 6.0% deduction).
  • Any work turned in 1,000 minutes (16 hours, 40 minutes) late is effectively zeroed, as that would be a 100.0% deduction.

Furthermore, whether availing yourself of your semester-long allowance (partially or fully) or not, the absolute latest any single assignment may be turned in for credit is 72 hours from its original deadline. Gradescope will not allow any submissions after that point, nor will the course ordinarily accept them via some other means.

Late work will not be accepted for the exam, the quizzes, or the final.

Extension Policy

Given the flexibility of the lateness policy, above, the course does not allow for extensions of any kind on its projects. Exceptions to this policy will be considered only in situations of documented medical or family emergency. Extensions that are only requested after a project’s deadline will not be considered at all. In these situations, communication with the course staff is paramount. The course rarely grants extensions retroactively, and so it is imperative you be in touch about your need for an extension promptly. The only individual authorized to grant extensions is the head teaching fellow; please be sure to include any relevant documentation in your request.


The Accessibility Services Office (ASO) is available to support all students who require accommodations due to disabling conditions; all such accommodations must be approved and coordinated by the ASO. If you require accommodations, please contact the ASO at 617-998-9640, or by email at

Academic Honesty

This course’s philosophy on academic honesty is best stated as “be reasonable.” The course recognizes that interactions with classmates and others can facilitate mastery of the course’s material. However, there remains a line between enlisting the help of another and submitting the work of another. This policy characterizes both sides of that line.

The essence of all work that you submit to this course must be your own. Collaboration on assignments and projects is not permitted except to the extent that you may ask classmates and others for help so long as that help does not reduce to another doing your work for you. Generally speaking, when asking for help, you may show your work to classmates and others, but you may not view theirs, so long as you and they respect this policy’s other constraints.

Below are rules of thumb that (inexhaustively) characterize acts that the course considers reasonable and not reasonable. If in doubt as to whether some act is reasonable, do not commit it until you solicit and receive approval in writing from the course’s instructor. Acts considered not reasonable by the course are handled harshly.

If you commit some act that is not reasonable but bring it to the attention of the course’s instructor within 72 hours, the course may impose local sanctions that may include a failing grade for work submitted, but the course will not escalate the matter further except in cases of repeated acts.


  • Communicating with classmates about assignments in English (or some other spoken language), and properly citing those discussions.
  • Discussing the course’s material with others in order to understand it better.
  • Helping a classmate identify a bug in their code at office hours, elsewhere, or even online, as by viewing, compiling, or running their code after you have submitted that portion of the assignment yourself, provided that you add a citation to your own code of the help you provided and resubmit yourself.
  • Incorporating a few lines of code that you find online or elsewhere into your own code, provided that those lines are not themselves solutions to assigned problems and that you cite the lines’ origins.
  • Sending or showing code that you’ve written to someone, possibly a classmate, so that he or she might help you identify and fix a bug, provided you properly cite the help.
  • Submitting the same or similar work to this course that you have submitted previously to this course, CS50 AP, or CS50x.
  • Turning to the course’s heads for help or receiving help from the course’s heads during the exam.
  • Turning to the web or elsewhere for instruction beyond the course’s own, for references, and for solutions to technical difficulties, but not for outright solutions to assignments.
  • Using CS50’s own AI-based software, including the CS50 Duck (ddb) in and as well as in Ed.
  • Whiteboarding solutions to assignments with others using diagrams or pseudocode but not actual code.
  • Working with (and even paying) a tutor to help you with the course, provided the tutor does not do your work for you.

Not Reasonable

  • Accessing a solution to some assignment prior to its deadline.
  • Accessing or attempting to access, without permission, an account not your own.
  • Asking a classmate to see their solution to an assignment before its deadline.
  • Discovering but failing to disclose to the course’s heads bugs in the course’s software that affect scores.
  • Decompiling, deobfuscating, or disassembling the staff’s solutions to assignments.
  • Failing to cite (as with comments) the origins of code or techniques that you discover outside of the course’s own lessons and integrate into your own work, even while respecting this policy’s other constraints.
  • Giving or showing to a classmate a solution to an assignment when it is he or she, and not you, who is struggling to solve it.
  • Looking at another individual’s work during the quizzes or exam.
  • Manipulating or attempting to manipulate scores artificially, as by exploiting bugs or formulas in the course’s software.
  • Paying or offering to pay an individual for work that you may submit as (part of) your own.
  • Providing or making available solutions to assignments to individuals who might take this course in the future.
  • Searching for or soliciting outright solutions to assignments online or elsewhere.
  • Splitting an assignment’s workload with another individual and combining your work.
  • Submitting (after possibly modifying) the work of another individual beyond the few lines allowed herein.
  • Submitting the same or similar work to this course that you have submitted or will submit to another.
  • Submitting work to this course that you intend to use outside of the course (e.g., for a job) without prior approval from the course’s heads.
  • Turning to humans (besides the course’s heads) for help or receiving help from humans (besides the course’s heads) during the quizzes or test.
  • Using AI-based software other than CS50’s own (e.g., ChatGPT, GitHub Copilot, Bing Chat, et al.) that suggests or completes answers to questions or lines of code.
  • Viewing another’s solution to an assignment’s problem and basing your own solution on it.
  • Viewing the solution to a lab before trying to solve it yourself.

Acknowledgement and Authorization

Harvard plans to record audio, photos, and video of Computer Science 50 (CS50) lectures, sections, office hours, seminars, and other events and activities related to CS50 (the “Recordings”), with the aims of making the content of the course more widely available and contributing to public understanding of innovative learning (the “Projects”). As part of the Projects, the Recordings, or edited versions of them, may be made available to other Harvard students, to students at other educational institutions, and to the broader public via edX, the Internet, television, theatrical distribution, digital media, or other means. One of the ways it is expected that the Recordings, or edited versions of them, will be made publicly available is under a Creative Commons Attribution-NonCommercial-ShareAlike (CC BY-NC-SA) license. Another example is that Harvard may make and disseminate montages of “memories” from the class with images from the Recordings. The Recordings also may be used to make other derivative works in the future. Students may elect not to appear in photos and video used in the Projects and may still participate fully in CS50.

To attend CS50, you will need to sign online an Acknowledgement and Authorization in the following form:

I understand and agree that, if I do not wish any photos or video of me to be used as part of the Projects:

  • If I am participating in CS50 in a classroom or other course location, I should sit in the designated “no-film” zone of the classroom or location, and should not walk in the field of view of the cameras.
  • If I am participating in CS50 online, I should turn off my own camera and should not display a photo of myself. In addition, if I do not wish my real name to be displayed when I speak and my voice is recorded, I should select a pseudonymous user name in Zoom (or other online service). If I select a pseudonymous user name, I will inform the instructor, so the instructor knows who I am.

I understand that I am free not to be included in the Projects’ photos and video in this way, and that this will not affect my grade or my ability to participate in course activities.

Unless I exclude myself from the Projects’ photos and video as described above and take any other steps outlined by the instructor to avoid being filmed, I authorize Harvard and its designees to make and use Recordings of my participation in CS50 and activities related to CS50. I understand and agree that the Recordings may include my image, name, and voice. I also understand and agree that, even if I opt out of the Projects’ photos and video and choose a pseudonymous user name, my voice will be recorded if I am participating online, and may be picked up by microphones outside the “no-film” zone if I am in a CS50 classroom or other location, and my spoken name also may be included in the Recordings. If the class is online, I may participate instead via chat messages, which will not be included in the Recordings.

I understand and agree that Harvard and its designees will have the irrevocable, worldwide right to make, edit, modify, copy, publish, transmit, distribute, sell, publicly display, publicly perform, and otherwise use and make available the Recordings and any other works that may be derived from those Recordings, in any manner or medium now known or later invented, in connection with the Projects, and to authorize others to do so as well. I hereby transfer to Harvard any rights, including copyrights, I may have in the Recordings that Harvard makes. I will remain free to use and disseminate any ideas, remarks, or other material that I may contribute to course discussions.

I acknowledge and agree that I will not be entitled to any payment, now or in the future, in connection with the Recordings or any works derived from them. This Acknowledgment and Authorization is a binding agreement, and is signed as a document under seal governed by the laws of the Commonwealth of Massachusetts.

Unless you exclude yourself as described in the Acknowledgment and Authorization, you are agreeing, by attending CS50, that your participation in CS50 and related activities may be recorded and used by Harvard in connection with the Projects without further obligation or liability to you, even if you do not sign any authorization.

If you have any questions about the above, contact