Internet-Security.com UDP port 1026 details

Microsoft Windows Messenger Service (the legacy service used by the net send command on Windows NT/2000/XP) was commonly reachable on UDP port 1026 due to its RPC dynamic port assignment, and many systems received Messenger messages on UDP 1026/1027.
In the early 2000s, spammers abused this by sending unsolicited UDP datagrams to port 1026 to trigger pop-up ads on vulnerable Windows machines; Microsoft mitigated this by disabling the service by default in Windows XP SP2, and admins often blocked UDP 1026–1028.
Beyond that historical Windows Messenger Service traffic, there are no widely recognized mainstream applications that legitimately rely on UDP 1026.

UDP 1026