UBB.threads PHP Forum Software Community Forums UBB.classic UBB.classic 6 Support Virus affecting homepage URL?

Same EXACT happened on my UBB 6.5. A porno page was entered as a home page on the profile. I deleted and emailed the guy. He pleaded with me that his computer has a virus and is doing this. The guy has been posting on my site and seems like a normal guy, not a troublemaker.