Yahoo Messenger may open port 5050/tcp on the system, creating a security risk. If this port is blocked, Yahoo Messenger searches the firewall for any open port, such as 80, and uses that port.
The use of Internet-based messaging services poses a risk because there are no methods used to determine which traffic should be allowed or blocked before reaching the user. An attacker could utilize Yahoo Messenger to gain access to the system, execute code, or propagate malicious code using social engineering methods.
Administrators should review security policies to determine if Internet-based messaging services are allowed on corporate network systems.