One our favorite tools has been compromised. Piriform is reporting CCleaner 5.33.6162 and CCleaner Cloud 1.0.7.3191 are the affected versions.
The software was modified unknowingly before release. Once installed the malware is able to report back your computer name, OS version, IP address, software packages, and MAC addresses of your first three NICs.
Piriform recommends upgrading to version 5.34 for local installations. Cloud users should already have the update applied. Grab the latest version here.