Eliminate take-home exams. As for collections of answers or old tests, those have always been around and generally aren't considered cheating. In fact they're good preparation for allowing students to get familiar with the testing environment.

But there's no excuse for lazy professors/instructors and each new test should be distinct. Re-using an old test or old test questions is questionable behavior by a professor.

I agree with what Veen posted earlier: the cheating students should be expelled.