This indicates an attack attempt to exploit a Denial of Service vulnerability in Microsoft Office 2010 beta.
The vulnerability is a result of the application's failure to properly sanitize user supplied inputs, which allows remote attackers to cause a denial of service (memory consumption) via a large number of SIP INVITE requests. The signature detects for 100 requests within 5 seconds.
Microsoft Office 2010 beta
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.