A recent version of the popular Windows cleanup tool CCleaner contains malware, apparently added by malicious persons who gained access to a server used by the software developer, Piriform.

The malware was found only in the 32-bit version of CCleaner 5.33.6162. No other versions were affected.

Piriform reacted quickly to the discovery, and yesterday released a new version: CCleaner 5.34.

If you have CCleaner installed on any Windows computers, you should make sure you’re running version 5.34, and if not, install it as soon as possible.

Update 2017Sep23: The server that was breached is actually managed by Avast, which purchased CCleaner software developer Piriform in July.

Ongoing analysis of the hack revealed that this may have been a state-sponsored attack, and that it specifically targeted high profile technology companies. Apparently the malware in the compromised version of CCleaner contained a second payload that was only installed on about twenty computers at eight tech companies.