It's quite possibly a virus or trojan. I suggest you do several full system scans, using the resources in this thread
. Also try closing all external programs before running mIRC.
Please note, mIRC is not a file trading program, it's a chat program. It'd be nice if you stopped abusing it
Furthermore, if this is happening in other IRC clients, it really isn't an mIRC bug. mIRC/Khaled is not the owner/creator of the DCC protocol.