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Event ID 4787: A non-member was added to a basic application group

Windows Event ID Lookup: What Windows event IDs mean: 4625, 4624, 4740, 6008, 41, 7045, 1102 and 3,000 more, with Windows' own message text, the fields and what to check.

Look up a Windows event ID from Event Viewer, a SIEM alert or a log export: what it means, the fields it records, and what to check. Many IDs are used by more than one source (event 41 is both a Kernel-Power crash and a boot error), so every definition is shown, the one people usually mean first. The message text is Windows' own, read from the event providers of Windows 10.0.26200.0, 2026-10-28; the notes are ours, based on Microsoft's security auditing reference.

Try: 4625, 4624, 4740, 6008, 41, 1074, 7045, 1102, 4104, 1149

A non-member was added to a basic application group.

Event 4787
Security-Auditing
Security log
Audit
Message and fields (as Event Viewer shows them) 
A non-member was added to a basic application group.

Subject:
	Security ID:		…
	Account Name:		…
	Account Domain:		…
	Logon ID:		…

Member:
	Security ID:		…
	Account Name:		…

Group:
	Security ID:		…
	Account Name:		…
	Account Domain:		…

Additional Information:
	Privileges:		…

A non-member is an account that is explicitly excluded from membership in a basic application group.  Even if the account is specified as a member of the application group, either explicitly or through nested group membership, the account will not be treated as a group member if it is listed as a non-member.