Got this popup while surfing on 2+2. I did not press OK, in fact I was even scared to close it myself. Instead I opened up Windows Task Manager and ended the application from there. It listed itself as AVG - Windows Explorer, but in fact is malware trying to install itself when activated.
I found this on the interwebs (links intentionally deleted) :
The malware comes from this link : http:// XXXXXXXX.com/