In a blog post, Piriform confirmed that two programs released in August were compromised. 'There is nothing a user could have noticed,' Williams said, noting that the optimization software had a proper digital certificate, which means that other computers automatically trust the program.

Talos researcher Craig Williams said it was a sophisticated attack because it penetrated an established and trusted supplier in a manner similar to June's “NotPetya” attack on companies that downloaded infected Ukrainian accounting software. At the time of the acquisition, the company said 130 million people used CCleaner.Ī version of CCleaner downloaded in August and September included remote administration tools that tried to connect to several unregistered web pages, presumably to download additional unauthorized programs, security researchers at Cisco's Talos unit said. The malicious program was slipped into legitimate software called CCleaner, which cleans up junk programs and advertising cookies to speed up devices.ĬCleaner is the main product made by London's Piriform, which was bought in July by Prague-based Avast, one of the world’s largest computer security vendors. This came after security researchers at Cisco Systems Inc and Morphisec Ltd alerted Piriform's parent Avast Software of the hack last week. Piriform said it worked with law enforcement and cut off communication to the servers before any malicious commands were detected. More than 2 million people downloaded tainted versions of Piriform's program, which then directed the computers to get instructions from servers under the hacker's control, Piriform said.

SAN FRANCISCO - Hackers broke into British company Piriform Ltd's free software that optimizes computer performance last month, potentially allowing them to control the devices of millions of users, the company and independent researchers said on Monday.

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