[CentOS] DROP MSN MESSENGER by IPTABLES- CENTOS 4

Dear Friends,

I installed CENTOS 4.4 on server.

I need DROP MSN Messenger using IPTABLES,  I created the rule below.

$IPTABLES -A INPUT -p tcp -m string --string "x-msn-messenger" -j DROP



But, When I run IPTABLES, I have received follow error:

DROP -> MSN Messenger
iptables v1.2.11: Couldn't load match 
`string':/lib/iptables/libipt_string.so: cannot open shared object file: 
No such file or directory


Where DO I find library libipt_string ?



Thanks for help.


Adriano Frare