balcklisting ip's

I think blacklisting ip's will be very tricky job. I agree with Mathew as we
are living in cable/dsl modems. They use DHCP and ip can be reassigned to
different users in given range despite its blocking problem with NAT. You
can imagine a scenario you block ip 1.2.3.4 (Hypothetically) and that is
assigned to Mr. X. After lease expires that is assigned to Mr. Y. Now Mr. Y
is blocked from accessing with no fault of his own and Mr. X is still
trouble for us.
I think using confirmation email for user and increasing warning level of
user in case of malicious activity is better option. We can block user after
certain level of warning and send him account deletion mail.
We need to make some blacklist of words that is prohibited on forums that
can used to increase warning level of user.


Arun