FBHole is a worm in Facebook. However, it doesn't seem to be doing anything else than posting a message to people's Facebook walls.
The message that the worm posts is "try not to laugh xD http://www.fbhole. com/omg/allow.php?s=a&r=[random number]"
If you follow the link, you end up on a page that looks like this:
The page shows a fake error message. If you click anywhere on the page, you will trigger a script that will try to post the same message to your Facebook wall. This is done with an invisible iframe that follows your mouse around — causing you to click on an invisible "publish" button. In addition to the wall message post, nothing else happens.
The worm is spreading like wildfire. To get some idea, try this public search via youropenbook.org.
We have blocked domain fbhole.com so that F-Secure Internet Security users cannot access it. The domain was registered yesterday and it points to an IP address in Czech Republic, shared by another Czech site called ironbrain.net.
Updated to add: Domain fbhole.com shared an IP address with ironbrain.net [22.214.171.124]. Ironbrain.net hosted a website with references to Facebook but no obvious illegal content. While fbhole.com was registered with privacy protection, ironbrain.net had contact information in the WHOIS database, complete with a Czech phone number.