In other words, the people behind CCleaner don't think any of the 2.27 million people who downloaded and ran the 5.33.6162 version of CCleaner and the 1.07.3191 version of CCleaner Cloud have actually been harmed by this malware.
Piriform, which develops the CCleaner software created to remove unwanted files from Android phones and Windows PCs, said it had identified "suspicious activity" in two versions of the program which it found had been "illegally modified".
Hackers managed to hijack a popular PC cleanup tool, CCleaner, meaning that anyone who downloaded or updated it between mid-August to mid-September also downloaded malware without realising it.
The malware was being installed by version 5.33.6162 of CCleaner, a utility for speeding up PCs and Android devices, and version 1.07.3191 of CCleaner Cloud, according to Piriform.
The company believes it was able to disarm the malware before it harmed users.
Although malware of all types is most commonly spread through phishing attacks like infected attachments and phony links, a tactic which is seeing a lot of success is infecting trusted platforms. "We have no indications that any other data has been sent to the server.", Piriform stated in a blog post.
The postal and telecommunications recommends that you temporarily unable to use the program "CCleaner".
CCleaner software hacked to spread 'backdoor' malware to more than 2 million people
The Talos team wrote in an in-depth research analysis: "In reviewing the version history page on the CCleaner download site, it appears that the affected version (5.33) was released on 15 August 2017".
Avast owned CCleaner hasn't been clean itself for the past month, with hackers piggybacking malware on the software for at least a month.
"Supply chain attacks are a very effective way to distribute malicious software into target organizations", Cisco's threat intelligence group, Talos, explained in a blog about the hack.
Popular security company Avast bought CCleaner from Piriform in July. The Talos team noticed on September 13 that the installer for CCleaner v5.33 was triggering its malware protection systems.
Antivirus detection for the threat is extremely low, so even if you have downloaded and installed one of the affected CCleaner versions or have upgraded to them, it's likely that your computer has been backdoored. Such a backdoor is capable of receiving and running code from an attacker command and control server. Piriform did not immediately respond to a request for comment on the attack's distribution and where most affected systems were located.
An investigation into how the code was inserted into the program is underway, Piriform says, and Avast is unsurprisingly involved in trying to work out what has gone on here (we've reached out to the latter for comment on this incident, and will update this story if we hear back).
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