"The first victim regions to be hit with the Blackhole stuff were the U.S., the Russian Federation, Belarus, Germany, the Ukraine and Moldova," Kaspersky senior security researcher Kurt Baumgartner said Tuesday in a .

Blackhole is one of the most popular of the commercial exploit toolkits that cybercriminals use to automatically infect computers with malware when their owners visit malicious or compromised websites.

Blackhole is sold on the underground market and comes packed with a variety of exploits for known vulnerabilities in browser plug-ins such as Java, Adobe Reader and Flash Player.

After a reliable exploit for -- now identified as CVE-2012-4681 -- was released on Monday, many security researchers warned that cybercriminals would soon start targeting the flaw on a large scale.

Rumors that the exploit had been integrated into Blackhole started circulating on Tuesday morning after the toolkit's creator allegedly posted on an underground forum.