The massive malvertising campaign started with injected code into the ads served on the sites, and were delivered from several domains, all resolving to the following IP address: 184.108.40.206.
The domains, googlecodehosting.com/.org/.net and openxadvertising.com, are now blocked, but were serving malware pulled from compromised WordPress sites for several days.
The compromised sites were an assortment of random small and medium-sized sites, and among them was the official site for Government Security News.
"Referers for the GSN site appeared as early as Jun 14th, suggesting that the site was likely compromised for a couple of days before they became aware of the situation and took steps to clean the site," the researchers pointed out.
Unlucky visitors that clicked on the malicious ads would ultimately be asked to download a specially crafted .jar file that would take advantage (if possible) of two Java flaws and ultimately install the Zero Access Trojan on the victims' computer.
Given the similarity of the campaign to one executed in early May, chances are that the same cyber crooks are behind this one.