Software hack affected 2 million cpus

(CNN) - Hackers have targeted a type of personal computer cleaning software.

Security researchers and Piriform said hackers compromised CCleaner in a sophisticated attack that affected more than 2 million computers.

CCleaner deletes unneeded files and web browser caches to keep windows computers free of junk, but hackers were able to successfully place malware into a new version, released in August. 

Piriform said Tuesday that the company dealt with the sophisicated hack quickly once it was discovered, though it took four weeks to discover it.

"Within approximately 72 hours of discovery, the issue was resolved by Avast with no known harm to our Piriform customers," the company said in an update on Tuesday.

The hack may have started July 3, Piriform said.

PIriform advised Windows users to check if they are running compromised versions, delete the app and install the new, safe version. 

"And due to the proactive approach to update as many users as possible, we are now down to 730,000 users still using the affected version (5.33.6162). These users should upgrade even though they are not at risk as the malware has been disabled on the server side," Piriform said.

Copyright 2017 CNN. All rights reserved. Raycom News Network contributed to this report.