This must be not a new attack (I’ve found an almost year old article that mentions gcounter iframes) but I started to notice it this past weekend. First, on the Google’s Webmaster Forums, then in the Unmask Parasites logs. So I guess it’s a new wave of the attack.
When I first encountered a site infected by gcounter, I checked it with Unmask Parasites. Nothing suspicious was found except for the fact that the domain name was blacklisted by Google. I checked the diagnostic page and found this clue:
Malicious software is hosted on 1 domain(s), including gcounter.cn/.