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Employees at more than 500 companies have fallen victim to domain attacks in the last month, underscoring the increasing popularity of the tactic among Internet fraudsters, security experts said this week.

The attacks aim to redirect consumers to potentially malicious web servers by changing the records used to convert domain names to numerical addresses. Known as domain-name system (DNS) cache poisoning, the decade-old technique has been repurposed as another way for online fraudsters to install aggressive advertising software, or adware, on victims' computers and redirect people to pay-per-click Web sites.

"Over the last two years, we have seen a progression from hobbyist virus writers to people who are trying to make money," said Kyle Haugsness, a security incident handler for the Internet Storm Center, which has been tracking the latest spate of attacks. "The goal is to make the most money in the shortest amount of time."

Phishing attacks use email to attempt to lure users to click on a link, sending the victim to an attacker-controlled site. The latest type of attack, sometimes referred to as pharming, redirects a victim trying to go to popular legitimate sites instead to a malicious website or a pay-per-click website.

"We see the pharming attacks as being very effective as the next wave of phishing," said Richard Stiennon, vice president of threat research for Webroot Software, an anti-spyware software maker. While many Internet users might not fall victim to a fraudulent email message, a well executed pharming attack can be much harder to detect, he said.

"If we logged into our bank (and were redirected), we might not recognize where we were going before it's too late," he said.

Stiennon also stressed that money is the primary motive. Data from adware firms indicate that each PC installed with the software accounts for about $2.40 in annual revenue, he said. Pairing that data withWebroot's findings that the average PC scanned with the company's software has 2.5 adware programs suggests that adware firms garner nearly $2bn in annual revenue, or about 20 per cent of the more traditional online advertising market.

The Internet Storm Center, which collects and analyzes firewall log data to detect Internet threats, found that at least three attacks have used DNS cache poisoning since early March. Two of the attacks aimed to drive victims to adware installation sites, while the other appeared only to redirect browsers to a Web site advertising herbal supplements. From the Internet addresses included in one of the logs sent to the ISC, Haugsness estimates that between 500 and 1,000 companies were affected by the attacks in March.

Only one attack, which started April 1, continues to be a problem, ISC's Haugsness said. Yet, because the group does not know the full extent of the problem, it raised its online-threat condition to yellow on Tuesday.

"Some people were holding out -- we keep getting reports," Haugsness said. "We only received 25 e-mails from people on March 4, but we have information that it is way bigger."

The attackers have targeted corporate domain name servers that convert an employee's Internet requests from names to numerical addresses. The initial attack concentrated on compromising DNS servers using a known, and patched, vulnerability in gateway products from security company Symantec. (SecurityFocus is a subsidiary of Symantec.) Later attacks concentrated on exploiting DNS servers running on Windows NT and older versions of Windows 2000, which are vulnerable to certain exploits, Haugsness said.

No supported Microsoft products are vulnerable to DNS cache poisoning in their default configuration, the software giant said in a statement.

The attacks focused on redirecting local users from popular sites to attacker-owned sites.

One attack replaced the addresses of major financial, corporate and media Web sites with the addresses attacker-controlled servers. An employee at a company with a compromised DNS server would be redirected when attempting to view any of a the targeted Web sites, including American Express, Citibank, Fedex, OfficeMax, CNN and WebEx, to name a few. The sites themselves were not compromised.

A victim would be redirected to hostile web servers that attempted to use two exploits for Microsoft's Internet Explorer browser to load adware onto the person's computer, according to the Internet Storm Center's analysis.

Another attack used DNS cache poisoning to send any local .com request to another site. A victim would be redirected a number of times, eventually driving them to an affiliate-based pay-for-click network, according to an analysis completed by security firm LURHQ.

A representative of the pay-for-click firm could not immediately be reached for comment.

Such schemes will likely not end up in being very successful, as pay-for-click sites should be able to detect misuse, said Joe Stewart, a senior researcher at security firm LURHQ. Yet, the amount of money garnered from the attack is not a good measure of its impact, he said.

"Unfortunately there is no way to make a correlation between the amount of damage they are causing and the amount of money they are making," Stewart said. "They aren't making millions, but they are causing millions of dollars in damage."

Other attacks, such as a recent instant messaging worm, changes the local domain list, known as the hosts file, on the victim's computer. This has the same effect as DNS cache poisoning but only affects a single user. A program executed by a user with administrator privileges can change the hosts file.

Administrators should secure their DNS servers and make sure they are fully patched. New technologies such as security extensions for DNS still have a ways to go before they have some effect, Haugsness said.

"There are a lot of people that think DNS security extensions are going to be the fix for all the DNS problems," he said. "It is not widely deployed yet, so we don't know if that is going to be the case."

Copyright © 2005, SecurityFocus logo

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