[原文]mIRC DCC server protocol allows remote attackers to gain sensitive information such as alternate IRC nicknames via a "100 testing" message in a DCC connection request that cannot be ignored or canceled by the user, which may leak the alternate nickname in a response message.
mIRC DCC Server contains a flaw that may lead to an unauthorized information disclosure. The issue is triggered when a DCC session is initiated to the target, which will disclose the dcc-server's owner/nick resulting in a loss of confidentiality.
Upgrade to version 6.1 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.
Additionally, a new feature added in mIRC 6.1 allows you to change/spoof the nickname associated with a dcc send/get/chat/fserve:
/dcc nick -sgcf <oldnick> <newnick>