This indicates an attack attempt against a Denial of Service vulnerability in Microsoft Exchange.
The vulnerability is caused by an error when the vulnerable software handles a crafted UDP packet, leading to denial of service attack.
Microsoft Exchange 2000 Server Service Pack 3 with the Update Rollup of August 2004
Microsoft Exchange Server 2003 Service Pack 2
Denial of Service: Remote attackers can crash vulnerable service.
Apply patch, available from the website: