Hundreds of thousands of computers getting penetrated by a corrupted version of an ultra-common piece of security software was never going to end well. But now it's becoming clear exactly how bad the results of the recent CCleaner malware outbreak may be.

Researchers now believe that the hackers behind it were bent not only on mass infections, but on targeted espionage that tried to gain access to the networks of at least 20 tech firms. Earlier this week, security firms revealed that CCleaner, a piece of security software distributed by Czech company Avast, had been hijacked by hackers and loaded with a backdoor that evaded the company's security checks.