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Hackers who booby-trapped widely used security software also used their malware to infiltrate machines at tech firms, suggests analysis.
Millions of people downloaded a Windows version that hackers had laced with malicious code.
Cisco said the attackers were seeking valuable intellectual property.
Last week CCleaner creator Piriform revealed that attackers had managed to place a hijacked copy of version 5.33 that works on Windows on some download servers. The booby-trapped code was available for about a month between August and September,
Millions of people downloaded the compromised version of CCleaner but damage was limited because whoever created it had not updated it to include elements that could scan machines and steal data.However, Cisco said its analysis suggested that attackers had taken that extra step on machines at tech firms they had managed to infiltrate.
Hi-tech giants including Cisco, Intel, Google, Samsung and Microsoft were among the 20 or so