Hi,
In inline mode, the IPS (SSM-10) will bascially sits in the data path. All network traffic need to pass through the IPS to check/inspect and filter malicious traffic content like trojans, viruses, various types of network and application attacks and so on.
In short, IPS can/will intercept passing through network viruses, but not the one hovering outside the IPS, e.g viruses in end-user workstations.
So, in the event of viruses/worms outbreak where it tries to replicate itself all over the network, any passing through traffic (through IPS-SSM), e.g outbound to the internet, containing this malicious scripts will be stopped by IPS. However, for segments without IPS protection, no filtering can be done.
This combination allows you to handle viruses/worms/trojans issues both at the hosts level using host antivirus software, and at the network level using IPS appliance (or ASA with SSM).
FYI, Cisco partnered with TrendMicro to enhanced virus/malware protection in the new IPS 5.1.
http://www.cisco.com/en/US/partner/products/hw/vpndevc/ps4077/products_data_sheet0900aecd801eeea5.html
Rgds,
AK