[Digital Jedi]

It's showing up as Unknown Location because index.php isn't a known location in vBulletin. This happens sometimes when modifications to your board add custom pages or you've made a separate vB page your main domain; your landing page.

But even so, sometimes funny names (beyond the usual weird names people sometimes pick) are automated registrations. Either a spam bot looking to post, or looking to put links in its signature to help boost a particular sites search engine's rankings. Check the user's email. If it's also some kind of gibberish, a bizarre or foreign domain name (particularly .ru, if you're not expecting a lot of registrations from Russia) and/or if his signature has some weird links to it (like links to cheap plastic surgery, affordable real estate cheap brand name products, etc), then it's probably a spam bot.

Trust me, hackers won't show up in Who's Online.