Many sites offering "cracked" software or "keygens" (key generators) bundle their downloads with hidden malware. This can lead to identity theft or your files being locked by ransomware.

Additional features included with a professional license are: Driver Updater

A serial key, also known as a product key, is a unique code used to activate and register CCleaner Professional 6.17. The serial key is required to unlock the full features of the software, including:

: CCleaner uses online validation; unofficial keys are frequently blacklisted, causing the software to revert to the free version or stop working entirely. Missing Updates

: On already-activated machines, the key may be stored in the registry at HKEY_LOCAL_MACHINE\SOFTWARE\Piriform\CCleaner (32-bit) or HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Piriform\CCleaner (64-bit). Activation Steps for Version 6.17 How do I manage my CCleaner subscription?