ASA5520 CPU Utilization in 98%

ASA5520 CPU Utilization in 98%

CPU utilization of The ASA 5520 in my company suddenly increased to 98%
for 2 hour. In this time, I have checked the logs:
Logs
Deny TCP reverse path check from 121.65.98.4 to 180.85.66.54 on interface
inside
I do not use this public IP address in my network. After I canceled
download in a PC, then the problem is resolved.
Could you please tel me what should I do that I will not faced with this
problem for future.