This horrible software has been around for quite some time. I have it pop-up on Firefox as well.
Currently, I block all these domain names at my router (all the same software/malware) - add dot com to the end of these (except the dot net one):
malware-scan
antivirusforall
drivecleaner
advancedcleaner
main-scanner
0scan
microantivirus2009
clearantispyware
onlineprivatescan
freeantivirus-online
yourantispywareplus
online-antivirus dot net
quick-scanner
Over time all of these domains have hosted the same malware. On Windoze, it installs and then falsely advises that you have a heap of viruses and asks you to "purchase" the full version to remove them - as somebody already pointed out.
It's difficult because I rarely see the same domain name twice.