I recently experienced a password-guessing attack. The inside Windows server's security was pretty well useless in stopping the attack (block, yes; stop, no), because the user ID kept changing, and Windows account lockout ignores source addresses. In this case, it was FTP, and I found an IPS signature for that, but it got me to thinking:
There don't seem to be password-guessing signatures for RDP, HTTP, HTTPS, or SSL. Granted it may not be practical for HTTPS and SSL, but what about the other two? Should we consider rolling our own?