A denial of service vulnerability exists in the implementation of the IDirectPlay4 application programming interface (API) of Microsoft DirectPlay because of a lack of robust packet validation. If a user is running a networked DirectPlay application, an attacker who successfully exploited this vulnerability could cause the DirectPlay application to fail. The user would have to restart the application to resume functionality.

http://www.microsoft.com/technet/security/bulletin/ms04-016.mspx