alert tcp $HOME_NET any -> $EXTERNAL_NET 25 (msg:"BLEEDING-EDGE VIRUS Forbot-FG SMTP Outbound"; flow:to_server,established; content:"UEsDBAoAAAAAA"; content:"LjP2AVbKEF"; distance:3; within:13; reference:url,www.sophos.com/virusinfo/analyses/w32forbotfg.html; classtype:trojan-activity; sid:2002369; rev:1;)