ipset

# install it
apt-get install ipset

# create a blacklist
ipset create blacklist hash:ip hashsize 4096

# add the blacklist to your iptables rules
iptables -I INPUT -m set --match-set blacklist src -j DROP
iptables -I FORWARD -m set --match-set blacklist src -j DROP

# check that rule is set in iptables
iptables -L

# now add the offending ip address
ipset add blacklist WW.XX.YY.ZZ

# check that the ip address is in your blacklist
ipset list blacklist