Phoenix and Blackhole are the most popular and widely used exploit kits because their creators are always tinkering with them and pushing out update and improved attack capabilities.

Blackhole's authors have been very productive lately as they not only added the still unpatched XML Core Services vulnerability to the pack, but also changed the JavaScript code that initiates the exploitation sequence so that it can dynamically generate new domain domains.

"If the location or URL for the iframe, which actually contains the malicious code, changes or is taken down, all of the compromised sites will have to be updated to point to this new location," Symantec's researchers explained the problem that has been fixed with this change.

"To deal with this, the Blackhole JavaScript code on compromised sites now dynamically generates pseudo-random domains based on the date and other information, and then creates an iframe pointing to the generated domain."

The researchers seem to have managed to discover the exact method of creation of these domains and can determine those that will be used in the future, but that knowledge is likely to be of small help in stopping the attacks in the long run.

"So far we have seen a small but steady stream of compromised domains using this technique. This suggests that this is perhaps some kind of trial or test that could be expanded in future," the added.