By default, when traffic is denied by an extended ACE or a Webtype ACE, the adaptive security appliance generates system message 106023 for each denied packet, in the following form:
%ASA|PIX-4-106023: Deny protocol src [interface_name:source_address/source_port] dst
interface_name:dest_address/dest_port [type {string}, code {code}] by access_group acl_id
If the adaptive security appliance is attacked, the number of system messages for denied packets can be very large. We recommend that you instead enable logging using system message 106100, which provides statistics for each ACE and lets you limit the number of system messages produced. Alternatively, you can disable all logging.
You can configure the logging for an Access Control Entry to know about packets arraving:
http://www.cisco.com/en/US/docs/security/asa/asa81/config/guide/traffic.html#wp1061688
