Polymorphic malware on the rise, says Sophos

A new generation of so-called polymorphic attacks - where malware repeatedly mutates to evade antivirus detection - are continuing to drive the growth in malware levels, say experts.

In its annual threat report, security firm Sophos said that the majority of samples it observes are unique attacks associated with polymorphic malware. The company said that roughly 75 percent of harvested samples are only spotted within one organisation and associated with a single attack.

The numbers suggest that polymorphic attacks, in which a malware sample edits its own source code to avoid signature-based detection, are on the rise and growing in popularity with cyber criminals.

"This level of polymorphism is unprecedented," the company said in the report.

"What’s more, attackers have begun to develop and use far more sophisticated approaches to polymorphism to hide their attacks from security vendors and IT organisations."

To combat the increase, Sophos said that it and other vendors have been forced to adopt new detection techniques. Among the tricks used by security researchers is seeking to detect the "engine" components malware writers use to obfuscate their code.

As the new detection tools are introduced, malware writers have also changed their tactics, introducing server-side polymorphic tricks which place the obfuscation components on a hosted server, allowing the malware to dial a host and obtain instructions for modifying itself.

"For certain SSP malware, the back-and-forth between security vendors and malware authors has accelerated dramatically," Sophos said.

"For example, sophisticated malware authors are constantly attempting to determine which portions of their code are being detected . We’ve seen attackers modify and replace compromised code within hours."

In addition to installing and maintaining security software, the company is advising administrators to monitor network traffic for suspicious behaviour. The company said that many malware attacks, including peer-to-peer infections, will show a tell-tale traffic pattern which can be spotted and blocked to prevent the spread of an infection.