Users of the popular program CCleaner for Windows are being warned today to, update the application immediately this because a backdoor which is open to hackers has been installed on the software. This malware then allows them to install other dangerous programs, like ransomware or key loggers, onto the infected machines.

According to Avast, who own CCleaner, 2.27 million users could have been affected by this incident. Avast are quick to add, however, that users should not worry.

CCleaner is a file cleaning tool that has been downloaded 2 billion times and averages about 5 million downloads a week.  The vulnerability was detected on September 13th in the version 5.33 of CCleaner.

Pirisform have said “To the best of our knowledge, we were able to disarm the threat before it was able to do any harm.”

Piriform explained that the malware was preparing a second phase that would do something “bigger” but that they were able to shut it down before the second phase could launch.