Good news for those of you with pirated copies of Windows XP: Microsoft is going to replace your pirated copies with legitimate ones. Their trade-in program offers full amnesty and will be good for up to five PCs.

The catch? You have to actually have bought your copy of XP, and must have done so thinking it was legitimate. Thinking it was or should be free for download isn’t enough. One goal, according to Microsoft, is to see where these pirated copies are coming from. As a result, you’ll have to roll-over on the person who sold it to you. But if you legitimately got ripped off, why wouldn’t you want to?

Apparently there are a lot of XP users who aren’t sure whether they own a legitimate license or not. Here’s a suggestion. If your activation key starts with “FCKGW,” then it probably isn’t.