For a secure and official activation, you should use a valid product key. Microsoft Support Hack7_v4: Windows 7 Activation Bypass | PDF - Scribd
Chew-WGA is a third-party activation tool designed to bypass Windows Genuine Advantage (WGA) chew wga windows 7 ultimate 64 bit
CHEW WGA works by patching the WGA validation files in Windows 7, allowing the operating system to bypass the validation process. This enables users to activate their Windows 7 Ultimate 64 bit installation without a valid product key. The tool modifies the WGA files, making it seem like the installation is genuine, and thereby tricking the WGA validation process. For a secure and official activation, you should
Microsoft no longer sells Windows 7 keys, but you can still: For a secure and official activation