Rule Example

alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS 80 (msg:"WEB-IIS ISAPI .ida access"; uricontent:".ida"; nocase; flags:A+; reference:arachnids,552; classtype:web-application-activity; reference:cve,CAN-2000-0071; sid:1242; rev:2;)

alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"SMTP expn root"; flow:to_server,established; content:"expn"; nocase; content:"root"; nocase; pcre:"/^expn\s+root/smi"; reference:arachnids,31; classtype:attempted-recon; sid:660; rev:7;)