Consider the following scenario:
In this scenario, you notice that worms are removed, but the messages are not purged as expected.
To resolve the problem, set the Max Container File Infections
value to a number instead of 0. Or, install Forefront Security for Exchange Server with Service Pack 2 (SP2)
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
Description of Forefront Security for Exchange Server with Service Pack 2