Piriform, the developer of CCleaner now owned by security firm Avast, says that its download servers were compromised at some point between 15 August, when it released version v5.33.6162 of the software, and 12 September, when it updated the servers with a new version.
In that period, a trojan was loaded into the download package which sent “non-sensitive data” from infected users’ computers back to a server located in the US. The data, according to Piriform, included “computer name, IP address, list of installed software, list of active software, list of network adapters”.
“Our new parent company, the security company Avast, determined on the 12th of September that the 32-bit version of our CCleaner v5.33.6162 and CCleaner Cloud v1.07.3191 products, which may have been used by up to 3% of our users, had been compromised in a sophisticated manner. Piriform CCleaner v5.33.6162 was released on the 15th of August, and a regularly scheduled update to CCleaner, without compromised code, was released on the 12th of September. CCleaner Cloud v1.07.3191 was released on the 24th of August, and updated with a version without compromised code on September 15. The compromise could cause the transmission of non-sensitive data (computer name, IP address, list of installed software, list of active software, list of network adapters) to a 3rd party computer server in the USA. We have no indications that any other data has been sent to the server. Working with US law enforcement, we caused this server to be shut down on the 15th of September before any known harm was done.
It would have been an impediment to the law enforcement agency’s investigation to have gone public with this before the server was disabled and we completed our initial assessment. Between the 12th and the 15th, we took immediate action to make sure that our Piriform CCleaner v5.33.6162 and CCleaner Cloud v1.07.3191 users were safe – we worked with download sites to remove CCleaner v5.33.6162, we pushed out a notification to update CCleaner users from v5.33.6162 to v5.34, we automatically updated those where it was possible to do so, and we automatically updated CCleaner Cloud users from v1.07.3191 to 1.07.3214.