From whatsnew.txt:
- Support for <a href="http://www.mirc.co.uk/ssl.html">SSL</a> has been added. You'll have to download some DLL's of OpenSSL 0.9.7c separately from mIRC and place them in the mIRC folder for this to work. mIRC will load the dll's automatically if it finds them, after which you can initiate a secure connection to an SSL capable IRC server. SSL settings can be found in the Connect/Options dialog, and are visible only when openssl dlls are loaded.