The group has made available a DDoS tool called the Low Orbit Ion Canon that just about anyone can use to participate in a DDoS attack. According to Correll, the tool gives users an easy way to hook their computers into a voluntary botnet of systems participating in a DDoS attack against specific targets at any given time.
Earlier this morning, a "voluntary botnet" of about 1,700 computers involved in the attack against MasterCard, Correll said. The group's member base appears to be growing, with about 2,200 participants present in an Anonymous chat room earlier today, more than double the 1,000 or so involved yesterday, Correll said. In some cases, in addition to the DDoS attacks, the group has resorted to Black Fax-ing, a practice in which a black sheet of paper is repeatedly sent to a fax recipient in order to deplete the machine's toner cartridge.
Meanwhile, Anonymous' own Web site, anonops.net, has been hit with massive counter-DDOS attacks and has been down intermittently the past few days, he added. Anonops.net is hosted by a Russian ISP.
Chet Wisniewski, a security researcher with Sophos Labs today said DDoS attacks continue to be the weapon of choice because they are relatively easy to pull off but hard to defend against.
DDoS attacks work by overwhelming targeted Web sites with useless traffic, rendering them inaccessible to others. One of the most effective ways of countering such attacks is by filtering out the useless traffic before it reaches the target, Wisniewski. Attack traffic such as that generated by Anonymous' relatively unsophisticated Low Orbit Ion Canon can be relatively easy to spot and block, he said.
Often, the impact of such attacks is less dramatic than it might appear. For instance, while MasterCard's main site may have been taken down today, none of the company's core business transactions have been touched, Wisniewski said.
For the attackers, "this is another form of political protest, even though it is criminal and something uncalled for," he said.
Jaikumar Vijayan covers data security and privacy issues, financial services security and e-voting for Computerworld. Follow Jaikumar on Twitter at @jaivijayan or subscribe to Jaikumar's RSS feed . His e-mail address is jvijayan@computerworld.com.