A multi-exploit hack pack was responsible for nearly three-fourths of all Web-based attacks during December, a security company said Tuesday.

Tagged with the moniker "Q406 Roll-up," the attack kit was behind 70.9% of last month's attacks, reported Atlanta, Ga.-based Exploit Prevention Labs. Up to a dozen different exploits make up the kit, which includes several exploits derived from the proof-of-concept code that researcher HD Moore published in July 2006 during his "Month of Browser Bugs" project.

It's difficult to tell the exact number of exploits in the package, said Exploit Prevention's chief technology officer, Roger Thompson, because the kit is heavily encrypted. The most common exploits found in the kit are setSlice, VML, XML, and (IE COM) Createcomobject Code.

"The dominance of this package reinforces the fact that the development and release of exploits frequently parallels legitimate software businesses," Thompson said in a statement. "The bad guys are working hard to update and release tweaks to existing exploits at least in part because developing a new exploit is a complex development task."

The nearest competitor to the Q406 Roll-up was a group of exploits collectively known as "MDAC" that takes advantage of vulnerabilities in multiple ActiveX controls to gain access to a victimized PC's hard drive and the files stored there. By Exploit Prevention's tally, MDAC accounted for only 5.7% of the Web attacks during December.

One long-time front runner, WebAttacker, disappeared from the list completely. It ranked second in Exploit's list as recently as November. "The bad guys have never really been successful with WebAttacker," Thompson said. "Their tweaks never quite worked. Most of the time, the variants were buggy and just shut down the browsers without infecting the PC."

Exploit Prevention Labs launched a line of exploit detection tools -- LinkScanner Lite and LinkScanner Pro -- in November. The former is free, while the latter is priced at $19.99 for a one-year subscription.