[jon-wood]

While it is indeed possible to cheat on the project itself to have any value that project gets followed up with an interview in which its discussed, and I think most people would trip up quite quickly if asked to explain in detail the process of developing some software they didn't in fact write.

[brbsix]

Exactly. Asking the candidate to outline the solution, the issues encountered, and the rationale behind the design should quickly illuminate any funny business. Depending on the scope of the project, you could even have them push code to a company repo real-time as they make progress. Obviously VCS histories can be rewritten in some circumstances, but I think it would help give a little more granularity as to how the work was done.