Okay, so. This is going to sound strange. One of our customers has been hit a few times, and we found an IP address associated with a download. Being the inquisitive fellow I am, I grabbed the file. I've run password crackers on zip files before, but this isn't likely to be using dictionary words, and I'm somewhat at a loss as to how long it'd take to brute force this file - Which is in itself only a few hundred kilobytes. Has anyone got any experience with zip file passwords?
There's some good options here, but I'd guess for a small zip that with a fast CPU you could probably bruteforce it relatively quickly, depending on how many characters they're using.