As many as five million Web sites hosted by Network Solutions have been serving up malware, probably for several months, a security expert said today.
"This is one of the biggest infections for drive-by download attacks that I've seen," said Wayne Huang, co-founder and CTO of Santa Clara, Calif.-based Armorize Technologies, a Web application security company.
Network Solutions disputed Huang's estimate of between 500,000 and 5 million infected sites, but was unable to provide its own count.
Huang said his firm's researchers initially tracked the infection to a widget installed by Network Solutions on its GrowSmartBusiness.com site, then later discovered that the same widget was installed by default on all "parked" domains hosted by the Herndon, Va. hosting giant.
Parked domains are those that have been registered, but lack any owner-provided content. Malware makers and scammers have used these under-construction sites in the past to spread attack code or artificially boost search site rankings to dupe consumers into visiting.
"The largest mass infection I can remember was 1.1 million pages," said Huang. "This is a lot bigger."
The widget turned every infected domain into a drive-by attack site that launched the multi-exploit "Nuke" toolkit against users running Internet Explorer, Firefox, Chrome and Opera. If the kit successfully hacked the browser, a Trojan downloader hit the Windows PC, searches were redirected and pop-up advertisements appeared.
Several of the antivirus programs that recognized the downloader identified it as a variant of "Koobface", a malware-spreading worm best known for attacking users of social networks such as Facebook.
Huang said that the attackers were making money by serving up the ads to infected machines, and further spreading the malware by copying the attack code to any of several peer-to-peer networks already installed on the system.
Additional malicious script was dropped into the infected sites that only targeted users in Taiwan and Hong Kong.
Using several search engines, Huang estimated that that infected widget appeared on between 500,000 and 5 million domains. Monday, he bet on the bigger of the two numbers. "Search engines are generally not keen on indexing parked domains," he said, saying that Yahoo and other search sites provided may thus undercount infected domains.
Network Solutions contested Huang's estimate. "The numbers reported over the weekend are not accurate," said company spokeswoman Susan Wade. "We're still investigating to determine the number affected."
Although Network Solutions has disabled the widget on all parked domains and has taken the GrowSmartBusiness.com site offline, the widget remains on approximately 5,700 active sites that manually installed it, Huang said. Nor has Network Solutions scrubbed the malicious script targeting users with IP addresses located in Taiwan and Hong Kong.
"If you have downloaded the GrowSmartBusiness widget to your website, we recommend you delete that widget and scan your site for malware," Network Solutions urged in a Monday security alert.
Huang traced the problem as far back as May, when Armorize blogged about a site hosted by Network Solutions that was serving malware to visitors. At the time, Armorize's researchers didn't realize the infection was widespread.
Wade said Network Solutions was still trying to determine an infection timeline.
It's possible that the multiple infections Network Solutions has acknowledged this year are related. In April, the hosting company dealt with a large-scale infection of WordPress-powered blogs, while in January several hundred sites it hosts were defaced.
"If these events were associated, then sometime in early April the attacker group must have decided to leverage the control they had of Network Solutions, and massively injected malicious content not into the default parked domain page, but rather, into the hosted WordPress blogs and/or sites," said Huang in a post to the Amorize blog on Saturday.
The attack on Network Solutions gave hackers a huge bang for their buck, said Huang, and may be a sign that they're targeting hosting firms.
"In the past, [attackers] have compromised sites with mass SQL injections where they try to corral every single site they can," Huang said. "But by attacking a hosting company, they can put backdoors with full control on millions of machines. There's no need to inject each site individually."
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, or subscribe to Gregg's RSS feed . His e-mail address is email@example.com.