I have seen this same thing few times before. All were very non-controversial websites. One in particular, I am aware of what it turned out to be. Someone joined the site, and added a link to malware in their profile. Google;s spider picked it up and flagged it. IE doesn't recognize the flag, and obviously neither does safari.
So, the admin merely looked at the new members for 2-3 days prior and found the spammer who did it. Because the profile also showed posts made and topics started, they saw he/she also posted the same link in an archived forum thread and started a new topic as well, that no one visited.
Those posts were removed, along with the new member (whose IP was also banned) and Google was asked to run back through it. They agreed and the flag was removed. It's a bot, or spider type thing that crawls the net and through websites, and flags automatically when links to malware (or redirects to sites with malware).
I'm not saying that's what this is, but maybe look back through the last few days of members and see who's who. The links in my friend's site were "shortened" URL's so be careful what you click if you see it.