Site hacked via this plugin

My site was hacked via this plugin enabling hackers to gain access to phpsendmail and distribute pornography via our wordpress installation.

FILE HIT LIST:
{CAV}PHP.Trojan.Spambot : /wp-content/plugins/tell-a-friend/ticketkRS.php
{HEX}php.cmdshell.unclassed.344 : /wp-content/plugins/tell-a-friend/tell-a-friend.php

tell-a-friend.php http://pastebin.com/nDKMMjMu

ticketRS.php http://pastebin.com/8xR03AAs

BIndex.php http://pastebin.com/6aMfuffN