Hackers have now targeted a type of PC cleaning software.
Security researchers and Piriform said hackers compromised CCleaner in a sophisticated attack that affected over two 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 advises windows users to check if they are running compromised versions, delete the app and install the new safe version.