HI .. you could try enabling the ips built-in signtures supported by the PIX. These are used to protect against common attacks.
" Cisco PIX Firewall includes an IP-only intrusion detection feature. It provides visibility at
network perimeters or for locations where additional security between network segments is
required.
The PIX IDS identifies more than 53 common attacks using signatures to detect patterns of
misuse in network traffic. Traffic passing through the PIX Firewall can be identified to be
audited, logged, and/or dropped.
After it is configured, the IDS feature watches packets and sessions as they flow through the
firewall, scanning each for a match with any of the IDS signatures. When suspicious activity
is detected, the PIX Firewall responds immediately and can be configured to do the following:
1. Send an alarm to a syslog server.
2. Drop the packet.
3. Reset the TCP connection. "
I suggest you check the command reference for the use of ip audit command !!!
I hope it helps .. please rate it if it does !!!