Windows 7 is officially unsupported by Microsoft. Use at your own risk. That said, Microsoft Security Essentials still works, as well as PC Matic, which i haven't used, but has a lot of positive reviews.

Microsoft no longer officially offers any public sources for Windows 7 ISOs, but these links still work as of May 2022:

• Ultimate x64
• Ultimate x86

Unofficial downloads of Enterprise as of May 2022:

• Enterprise x64
• Enterprise x86

Additional ISOs are listed here.

There are some important update packages that may be required to get a new installation to a workable state (including the ability to find and download updates):

• The Windows Management Framework (WMF) includes updates for powershell (and the ISE), WinRM, and WMI. WMF requires .NET 4.5 (for v5).
• The .NET Framework might fail to install on the first attempt; KB4019990 has an update available.
• Old .NET Framework downloads are here, and the last .NET 4 build (4.8) can be downloaded directly here.

This update has two prereq packages, install these three packages in order:

• KB4474419
• KB4490628
• KB4516065

Install these in order:

• KB2533552
• KB4019990 (.NET)
• KB4532945 (.NET)
• KB4524157 (.NET)
• KB4534310
• KB4567409
• KB3191566 (WMF)
• KB4539601
• KB2574819
• KB2592687
• KB2830477
• KB2857650
• KB2913751
• KB3102429