Registered to winShadow, a Windows remote-control product; almost never seen now.
IANA registers 3261 as winshadow, the port of winShadow — a commercial Windows remote-control and remote-administration package in the same family as pcAnywhere and VNC. No protocol specification was ever published and the product has no meaningful present-day deployment, so the registration is the extent of the public record. If 3261 is open, the interesting question is whether it is genuinely winShadow or something unrelated squatting on the number.
Do not expose
If it is remote-control software, it is a full desktop takeover path with legacy authentication — keep it off public networks and prefer a VPN plus a maintained remote-access tool.
$ nc -vz TARGET 3261Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.