Block brute-force attack using lastb and iptables

Using linux lastb command, I found that my server is brute-force attacked from many different IPs around the world! I have developed an script to detect brute-force attackers by lastb and block them by iptables. Here is the script:

#!/bin/bash

cd /root/
windowSize=100
tresh=10
lastb | head -n $windowSize | awk '{print $3}' | uniq -c > .ips
nlines=`wc .ips -l | awk '{print $1}'`
END=`expr $nlines - 1 `
for i in `seq 0 $END`;
do
        range=`expr $nlines - $i`
        count=`tail .ips -n $range | head -n 1 | awk '{print $1}'`
        if [ $count -gt $tresh ] ; then
                IP=`tail .ips -n $range | head -n 1 | awk '{print $2}'`
                if [ ! -z .blips ] ; then
                        touch .blips
                fi ;
                blocked=`cat .blips | grep $IP -c`
                if [ $blocked = '0' ] ; then
                        echo blocking $IP
                        iptables -A INPUT -s $IP -j DROP
                        echo $IP >> .blips
                fi ;
        fi;
done
rm .ips

Can it cause any problem if I run this script by crond every hours?