Brian Krausz

I build internet things

How to Catch a Cheater

November 22, 2010

Update: I wanted to explicitly mention that these homeworks were basically puzzles, which is why Googling was off-limits.

Update 2: Thanks gzak for remembering the actual name of the problem. It’s “Finkleberg’s 101 Game” and a copy of the actual homework is here.

There’s a story making its way around the web about a professor catching 1/3 of his class cheating and the fallout from it (everyone retakes the midterm, people who admit to cheating have to take an ethics course). It reminded me of something one of my professors at Carnegie Mellon did in one of my Freshman year CS classes. This is a from-memory recount of it, exact details are probably slightly off.

For context:

  • The early homeworks in this class were basically puzzles, where if you’ve seen the style of problem before you more or less knew the answer. The goal was to expose us to these types of problems and teach us how to think them through properly.
  • We were explicitly told that searching online for answers to homeworks was forbidden.
  • One of our last homework’s problems began with something like “Commonly referred to as The Glorblar Problem, …” (I don’t remember the actual word he used, it seemed completely plausible)

We get to class one day and wait for the professor to start speaking. Today he just starts running through slides silently:

  1. “As many of you know, one of my hobbies is catching cheaters”
  2. A picture of the last homework with the phrase “The Glorblar Problem” circled
  3. A screenshot of Google with “The Glorblar Problem” in the search box
  4. A screenshot of the Google results, with the domain of the first result (which had the problem and correct solution) circled
  5. The whois result for that domain, with the professor’s name circled (you can hear a collective gulp as half the room realized what was coming next)
  6. The apache logs from the webserver, along with blurred-out reverse IP lookups for the entries

Then he started speaking. He told us he had access to the login records from the school’s public machines as well. Anyone who Googled the result should confess and take a 0 for the homework, otherwise he would report them to the dean and they’d fail his mandatory class.

A ton of students confessed. A lot of them were sent the link from a friend and many claimed not to have used it, but nobody could deny that they were caught cheating by the letter of the law.

The moral of the story is don’t fuck with Luis von Ahn, he will wreck you (no, I wasn’t one of the students who cheated, but that was one of the more impressive hacks I’d seen during college).

tl;dr — My professor made a honeypot for cheaters by planting a Google bombed phrase in his homework.

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