: Microsoft may revoke these keys at any time, leaving your OS unactivated.

: Many sellers on sites like Back Market or Newegg sell older "Grade A" refurbished PCs that come with a Windows 7 Pro license pre-installed and activated. 3. Use a Windows 10/11 Key (Downgrade Rights)

: These are often volume licenses (KMS) intended for businesses or MSDN keys meant for developers.