There are also a number of problems where it is possible to narrow down the answer fairly easily, then submit a limited number of guesses until you get the right answer without having really shown that it is right.
To some degree, they need to rely on the users to care enough not to "cheat." There is no way to completely avoid people doing things like this.
To some degree, they need to rely on the users to care enough not to "cheat." There is no way to completely avoid people doing things like this.