An ident server (also called an identd) is simply a program that's purpose is to tell any computer that 'asks' what user is currently using your computer. It's a throwback from the good old days when most internet connected computers were large mainframes at universities and the like which could have many people using them, and the identd's response was a trusted source. These days most identds, like mIRC's, simply respond with whatever the user has told it to respond with and so are not trusted and add virtually no security or useful information to the IRC server whatsoever. The only exception is that since some IRC servers require an identd to be running some trojans that use IRC will implement an identd (sometimes taking over mIRC's) and respond with a random ident. Since these idents are often random letters like rgklhnla it's possible that some kind of lexical analyser could take that response and decide if it's jibberish, and if it is, refuse the connection. Whether that's what happened with you, or whether your ident matched a specific ident known to be a trojan's (some less advanced trojans simply use an unchanging ident like 'elite2k' or whatever).
All things considered, an identd has very little practical value for user identification.
