The elusive "Rock Phish" group continues to be innovative. The group appears to have started using the "fast flux" method to fool researchers and elude detection, according to new security research.

Cambridge University security researchers Richard Clayton and Tyler Moore tracked 30,000 phishing reports that came in through Phish Tank, a clearinghouse that tracks phishing sites, between February and April 2007. They found a link between Rock Phish and the fast flux approach.

The researchers logged their findings, among other things, in a paper, "Examining the Impact of Website Takedown on Phishing," that computer science doctoral candidate Moore presented at the Anti-Phishing Work Group (APWG) eCrime Researchers Summit in Pittsburgh on Thursday.

Nobody knows exactly who or what Rock Phish are -- whether it's one person or a group of people -- but security researchers believe Rock Phish is behind as many as half of all phishing attacks on the Web. Fast flux is a method by which a domain name that phishers use has multiple IP addresses assigned to it. The phishers switch those domains quickly between the addresses so that it's not as easy to find or shut down the phishing sites.

With fast flux, once a phishing site is found, it's not simply a matter of going to ISP hosting the domain name to shut down the site; authorities must go to the domain name registrar, which is more time consuming and complex, Moore said.

"There is automated [site] replenishment," he said. "Once proxies are taken down, new ones are taken into the fold."

According to Clayton and Moore's findings, Rock Phish as a group and fast flux as a method are by far the most effective means of phishing. A connection between them would be troublesome for researchers trying to reduce the number of phishing attacks and track down offending parties.

In an interview after his presentation, Moore said evidence about the connection between Rock Phish and fast flux is inconclusive. However, after four weeks of tracking sites that had all the earmarks of being Rock Phish attacks, the fast-flux method started showing up in phishing reports, he said.

"They were burning through 400 IP addresses per week," Moore said. "It becomes impractically hard to take down these proxy machines."

Rock Phish attacks can be identified by researchers because of the way they operate, which is different than standard phishers. They use compromised machines as proxy servers that connect to a central server, which researchers call "the Mother Ship," rather than serving up sites directly from the compromised machines.

Whether the fast-flux activity Clayton and Moore identified is actually the work of Rock Phish or a copycat group or person acting like them remains to be seen, but overall phishers appear to be using fast flux more, Clayton said.

"Whether it's [Rock Phish] or separate gangs acting like them, and whether they all get together and drink at the pub and compare methods at night, we don't know because the police haven't caught them yet," he said.

In addition to a connection to fast flux, Clayton and Moore's research also found that Rock Phish's elusive methods allow its phishing sites to stay live a full day and a half longer than average phishing sites. This gives sites served by the group more opportunity to lure unsuspecting Web users into their traps.