Ok so that wasn't it. But it doesn't have to be you that's infected to be flagged for spam. It could be the last person to have your IP, or somebody could've used your IP in forged headers for spam. Most websites don't do that kind of filtering (I've only ever seen PD.net do it, but I know others do), so you likely wouldn't see it elsewhere. Just an FYI.It was definitely site-specific (not on my end). It said something about HLP/Their Host being partnered for some sort of 'awareness program', claiming that I had a virus and that I needed to click some link to fix it.
It didn't affect any other website, and my machine appears to be clean. I haven't seen it since that one time, either.