Hackers spread hidden malware to 2.27 million people via CCleaner

An app used by millions to optimise computer performance has been hit by a malware attack.

CCleaner is an application that helps upwards of two billion computer owners keep their devices optimised, by cleaning cookies, internet history and other temporary files, but now it's being used to spread malware to millions of users.

The latest version of the app infects PCs, it is believed, making them part of a botnet - slave computers that hackers can pull into DDoS attacks.

A version of CCleaner 5.33 downloaded in August included hidden malware, according to security investigators Cisco Talos. But CCleaner's owner, Avast Piriform, claimed it prevented the breach from harming customers.

The version of CCleaner tried to connect to several unregistered web pages, presumably to download other programs.

"On September 13 2017, Cisco Talos immediately notified Avast of our findings so that they could initiate appropriate response activities," Cisco Talos said in a blog post.

What makes this attack unusual is that it comes from a legitimate version of a trusted app.

"By exploiting the trust relationship between software vendors and the users of their software, attackers can benefit from users' inherent trust in the files and web servers used to distribute updates," the blog post continued.

However, the company that owns CCleaner, Avast Piriform, said the breach did not harm any of their customers.

"Piriform believes that these users are safe now as its investigation indicates it was able to disarm the threat before it was able to do any harm," said an Avast spokesperson.

But a Piriform spokesperson added: "We estimate that 2.27 million users had the affected software installed on 32-bit Windows machines."

But Cisco Talos says the malware could expose a wider security problem. "The presence of a valid digital signature on the malicious CCleaner binary may be indicative of a larger issue," the firm said.

Craig Williams, a researcher at Cisco Talos, said it counted as a sophisticated attack since it penetrated a trusted supplier. This is similar to June's NotPetya attack hidden in infected Ukrainian accounting software.

"There is nothing a user could have noticed," Williams said, noting that the optimisation software had a proper digital certificate, which means that other computers automatically trust the program.

This is just the latest hack in an increasingly exposed online world. From TalkTalk to Ashley Madison, major hacking and data breaches have been consistently damaging companies and their customers over the past few years, and anyone can be caught in the crossfire.