Very few files that are large enough to make this an issue are legal to download. As the sticky says, this isn't meant for illegally downloading files and we're not here to help people to do so.
I am very well aware of the fact that the this forum does not approve of illegal downloads on irc. But you forgot a vast amount of TV rips and open source programmes that are available on IRC and free to share. Because I am living in a non-english country, I often download TV series rips, because I don't like dubbed versions
Also, keep in mind that XDCC is a SCRIPT. It is not built into mIRC itself. It just uses the DCC protocol to send files. The only way MD5 built into mIRC would work would be with the RESUME option. And that's DCC related, not XDCC. XDCC scripts have to requirement to list the MD5 even if mIRC has something built in for it.
I know, and that's exactly what I am talking about. My post wasn't meant for Khaled, but for people, who write xdcc scripts. They should always include md5 checks in their scripts. Just didn't know where else to post. I think many people interested in irc are frequenting this forum, so hopefully they will read my post and reflect a little upon what I suggested