Rogue:Win32/FakeXPA, another of those fake rogue malware critters, has stolen the AVG logo to use on their pop-ups within browsers. It looks alarmingly real. Check out the details here on Softpedia.
It should be obvious if you see a pop-up and you do not use AVG Antivirus 2011. But for those who do have it installed, it only takes a moment to be caught with your proverbial pants down.