4000
ICQ / Diablo II
Medium RiskTCP/UDP — Messaging
Port Overview
Port Number
4000
Service Name
ICQ / Diablo II
Transport Protocol
TCP/UDP
Category
Messaging
Security Risk
Medium
Port Range
Registered (1024-49151)
What is Port 4000?
Port 4000 is associated with ICQ instant messaging (legacy) and Blizzard's Diablo II game server. Various custom applications also use this port as a default. It is in the registered port range and frequently appears in network scans due to its use by multiple different services.
TCP/UDP
Messaging
Security Considerations
Port 4000 (ICQ / Diablo II) is classified as medium risk. While this service is commonly exposed, consider using encrypted alternatives where available.
Recommendation: Keep the service updated. Monitor logs for unusual activity.