It does sound like a good way to interview a candidate. But I can see from the company's side it being a bit of a potential legal challenge issue. Depending on

It does sound like a good way to interview a candidate. But I can see from the company's side it being a bit of a potential legal challenge issue. Depending on what the problem is and how deep it goes into the codebase or whatever, you might get into proprietary process information that someone outside the company shouldn't have access to, possible IP access violations, etc. If it can be done in such a way to avoid those pitfalls, then it might be ok. But I bet it's a tricky challenge, and may be why it isn't done often?