Anno 2070 originally launched with a mandatory online connection. Your serial number was tied to your Ubisoft account. However, the game also stored a local “token” or “license file” on your hard drive so you didn’t have to re-enter the key every launch. That local file—sometimes informally called a key file—could become corrupted or be deleted by antivirus software, leading to the dreaded prompt: “Please enter a valid serial number.”
Avoid downloading "Key Generators," "Key Files," or "Cracks" from unofficial sites. These files are frequently used to distribute malware and will not provide a functional serial number for the game's online features. If you'd like, I can help you with: Resolving connection errors during activation. Locating specific game files for modding purposes. Linking your Steam and Ubisoft accounts. Anno 2070 Serial Number Key File
If you have the game installed but can’t find the key, it may still be in your Windows Registry. Open and navigate to: Anno 2070 originally launched with a mandatory online