It was commonly included in or updated via Windows XP, Vista, and Windows 7. ✅ Should you keep or remove it? Microsoft XML Core Services 4.0 - Microsoft Lifecycle

You likely didn't install this manually. It usually arrives in one of two ways:

Microsoft MSXML 4.20.9818.0 is a specific version of . It is an older system component used by legacy Windows applications to parse and process XML data. Critical Status: Obsolete and Insecure

This software is considered and a significant security risk.

Note. Support for XML Core Services 4.0 has ended. Support was only available for Service Pack 3. Microsoft Learn

Because it no longer receives updates, it is frequently flagged by security scanners (like Nessus or Qualys) as a vulnerability.

Older applications (like Toad for Oracle, SQL Server tools, or older games) install it as a necessary dependency.