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Two prominent Web sites that specialize in remote access software known as rootkits have been taken offline by a large distributed denial of service attack (DDoS). The take-down was allegedly ordered by a shadowy group of hackers and rootkit authors who took offense at criticisms of their software posted on the sites.

Rootkit.com, an established Web site run by security expert Greg Hoglund, has been offline for almost a week. Two other sites, operated by a prominent rootkit author known as "Holy Father," have also been taken down in the attacks, which are believed to be the work of a group of Bulgarian and Turkish hackers known as the SIS-Team, according to Hoglund, the chief executive officer of HBGary, Inc., an information technology software and services company.

The attack against Rootkit.com began on Tuesday, April 5, after someone using the name "ATmaCA" posted an inflammatory message to one of the discussion groups on the site that advertised a number of malicious remote-access software programs sold by SIS Team, including SIS-Downloader, ProAgent, and SIS-IExploiter, Hoglund says.

The programs are powerful spyware tools that, when combined, enable remote attackers to secretly compromise other machines using attack Web pages. The programs are sold online at Web sites like Spyinstructors.com and are popular with the people behind spam campaigns, who use the tools to plant remote-control programs that are then used to send out spam, Hoglund says.

The post by ATmaCA prompted curt responses from Rootkit.com members, who objected to authors using the discussion forum as a venue to advertise their commercial software. Other rootkits discussed on Rootkit.com are open source, and authors typically post links to their source code on the site, Hoglund says.

In the "flame war" that erupted between the SIS-Team members and the Rootkit.com contributors, questions were also raised about the quality of the SIS-Team products. Some Rootkit.com regulars alleged that the tools were poorly written and frequently crashed machines they ran on, Hoglund says.

Within hours of the first post from ATmaCA, the Rootkit.com Web site was under attack by a network of more than 500 compromised computers, or bots, that flooded the site with about 170,000 requests a second, making it unreachable for most Internet users, he says.

Two rootkit-focused Web sites operated by Holy Father were also downed by DDoS attacks after that person posted remarks critical of ATmaCA and SIS-Team, according to an e-mail from Holy Father.

Extortion Demands

In both cases, extortion e-mail was sent to the Web site owner following the DDoS attacks, saying that the Web site owners could end the attacks by posting public apologies to ATmaCA and SIS-Team on their Web sites, Hoglund and Holy Father say.

Hoglund, who is a noted security expert and author of the book "Exploiting Software," was working on Monday to bring the Rootkit.com Web site back online. He expressed outrage at the attacks, which he said were instigated by a group of immature hackers, and said that he would have taken the inflammatory post about ATmaCA and SIS-Team off Rootkit.com as a matter of policy.

"I find it very offensive that a public Web site that does nothing but share information is attacked by a bunch of immature children," he says. "These are hackers who can't stand on their own merits. They make claims for their software, and then can't argue about it, but just DDoS their critics off the Internet."

Rootkit.com has more than 25,000 registered users and about 30 regular contributors. Despite the reputation of rootkits as hacker tools, many of those who frequent the site are professional security experts and students who study computer security and use the rootkit source code available on the site to figure out ways to defend against rootkit programs, Hoglund says.