The UK’s National Health Service has been hit by a voracious, data-stealing worm that’s easily detected by off-the-shelf security software, according to researchers who directly observed the mass compromise.

Researchers from anti-virus provider Symantec have been monitoring the Qakbot worm since last May and have documented its behavior here and here. On Thursday, after infiltrating two of the six servers used to collect pilfered data from infected machines, they provided an update that didn't exactly instill confidence in the healthcare system.

“The logs show that there is a significant Qakbot infection on the National Health Service (NHS) network in the UK,” the Symantec update states. “This threat has managed to infect over 1,100 separate computers that are spread across multiple subnets within the NHS. We have attempted to contact the affected parties and have no evidence to show that any customer or patient data has been stolen.”

Not that Qakbot doesn’t have the ability to clean out the NHS if it wanted to. Over a two week period, the researchers observed 4 GB of stolen data being funneled to the monitored servers. Because that represents a fraction of the servers used by Qakbot, the amount of pilfered information is likely much higher.

Qakbot spreads through webpages that install malware by exploiting patched vulnerabilities in Microsoft’s Internet Explorer and Apple’s QuickTime software. It is able to self-propagate on local networks through file shares. It “moves slowly and with caution, trying not to bring attention to its presence,” according to the update.

The malware scours an infected machine’s hard drive for internet search histories, banking and payment card information and logon credentials for some dozen websites and then uploads them to one of the six servers. It also records the contents of data stored by a browser’s autocomplete feature.

“In a nutshell, if your computer is compromised, every bit of information you type into your browser will be stolen,” Symantec researchers wrote.

While Qakbot primarily targets home users, plenty of corporate and government machines are infected as well. In addition to the NHS, other government computers that are compromised are located in Brazil. The threat is easily detected by Symantec’s anti-virus product, and presumably software from plenty of other companies as well. ®