Your files could be encrypted and held for ransom [5.7].

If you bought a physical copy, the key is usually on a card or sticker inside the box [11]. Activation Steps for PC and Mac

Do you need help for a specific email address, or

Pirated versions can install backdoors to your system [5.7, 5.33].

To move your license to a new computer, simply install the free version on the new device and enter your existing key [5.16].

If you have a Pro Plus or Premium license, the same key can be used across multiple PCs, Macs, and Android devices [5.18, 5.21].

Activating your license transforms the free version into the Professional edition instantly. On Windows: and navigate to Options > About [5.8]. Click on Upgrade to Pro or Register/Enter Key [5.8, 5.14].

For a safe experience, always purchase your license through the Official CCleaner Website or authorized retailers like Kinguin [5.25]. Quick Troubleshooting