Why are packet filter firewalls not always a competent countermeasure against instant messaging (IM) attacks?
A.
They are the best type of countermeasure for this type of threat.
B.
They cause an internal denial of service when dealing with IM traffic.
C.
They can detect worms that are being transmitted through this traffic type.
D.
IM clients can reconfigure themselves to work on a port that is open on the firewall.
Explanation:
Many firewalls do not have the capability to scan for this type of
traffic to uncover suspicious activity. Blocking specific ports on the firewalls is
not usually effective because IM traffic can use common ports that need to be open
(HTTP port 80 and FTP port 21). Many IM clients will auto-configure themselves to
work on another port if their default port is unavailable and blocked by the
firewall.