Thank you Varun. That is what I figured.
I did however found a workaround by monitoring syslog messages # 733100 - 733105.
That way I can get some statistics of how often the threat detection is active.
Got the info from this link :
http://www.cisco.com/en/US/docs/security/asa/asa83/configuration/guide/protect_threat.html#wp1094068
Information About Scanning Threat Detection
A typical scanning attack consists of a host that tests the accessibility of every IP address in a subnet (by scanning through many hosts in the subnet or sweeping through many ports in a host or subnet). The scanning threat detection feature determines when a host is performing a scan. Unlike IPS scan detection that is based on traffic signatures, the adaptive security appliance scanning threat detection feature maintains an extensive database that contains host statistics that can be analyzed for scanning activity.
The host database tracks suspicious activity such as connections with no return activity, access of closed service ports, vulnerable TCP behaviors such as non-random IPID, and many more behaviors.
If the scanning threat rate is exceeded, then the adaptive security appliance sends a syslog message (733101), and optionally shuns the attacker. The adaptive security appliance tracks two types of rates: the average event rate over an interval, and the burst event rate over a shorter burst interval. The burst event rate is 1/30th of the average rate interval or 10 seconds, whichever is higher. For each event detected that is considered to be part of a scanning attack, the adaptive security appliance checks the average and burst rate limits. If either rate is exceeded for traffic sent from a host, then that host is considered to be an attacker. If either rate is exceeded for traffic received by a host, then that host is considered to be a target.
