alert tcp $HOME_NET any <> $EXTERNAL_NET any (msg:"ET CHAT MSN file transfer reject"; flow:established; content:"MSG "; depth:4; content:"Content-Type|3A|"; nocase; content:"text/x-msmsgsinvite"; distance:0; content:"Invitation-Command|3A|"; content:"CANCEL"; distance:0; content:"Cancel-Code|3A|"; nocase; content:"REJECT"; nocase; distance:0; classtype:policy-violation; sid:2001243; rev:5; metadata:created_at 2010_07_30, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)