On Jan 13th, Microsoft have released 3 security bulletins. Of these one that deals with ISA is a serious one (critical). If you are running ISA as a firewall in your organizations, you should consider patching it. Here are all of them for your reference.
a.) Vulnerability in Microsoft Internet Security and Acceleration Server 2000 H.323 Filter Could Allow Remote Code Execution (816458): http://www.microsoft.com/technet/treeview/?url=/technet/security/bulletin/MS04-001.asp
b.) Vulnerability in Exchange Server 2003 Could Lead to Privilege Escalation (832759): http://www.microsoft.com/technet/treeview/?url=/technet/security/bulletin/MS04-002.asp
c.) Buffer Overrun in MDAC Function Could Allow Code Execution (832483): http://www.microsoft.com/technet/treeview/?url=/technet/security/bulletin/MS04-003.asp