As you can see, there's been an application doing the rounds called "Error Check System" causing problems for lots of people.
A quick observation before going on - the name sounds an awful lot like those given to rogue security programs, isn't it? When I heard about this, I was convinced it'd pop open a rogue antispware cleaner once installed as an application. Anyway...on your notification panel, you'd see this:
A message that one of your friends "faced some errors" checking your profile. If you clicked "View the Errors", you'd be taken to an application installer page.
Once this was done, it would bombard your friends with invites to use the application.
Over....and over......and over again.
It seems Facebook has since killed the application off - it no longer exists (for the moment!) to install on your profile. Interestingly, the creators kept putting it back online under different Facebook application URLs until Facebook killed it off completely.
Besides incredibly annoying spam and some other potentially dubious (mis)uses of technology (many people report the app not showing up on the page where you'd remove applications, and others claim it installed without them hitting "Activate") it doesn't appear to have done anything too malicious.
However, Josh Lim covered this on his blog and I can't help but notice.....again.....well, check out this portion of his screenshot:
Click to Enlarge
Ignoring the "Fake!" he pasted over the logo, how similar to rogue antispyware tool stock graphics is that? I'm pretty sure I've seen that exact graphic used on a rogue tool / advert before, but of course there's so many of them around it would take a little while to confirm. If anybody wants to play "match the graphic to the rogue" in the meantime, be my guest!
Even more curious, someone (as if by magic) has manipulated search results so that anyone searching for "Error Check System" in Google will see this as the top entry:
Click it, and you're taken to an extremely aggressive set of rogue antivirus download pages.
Click to Enlarge
So even though the "threat" of Error Check System on Facebook has fallen by the wayside (until they come back, of course), you'll need to be careful if you go looking for more information on this particular incident over the coming weeks...