I generally go out of my way to support older versions of Windows, however Windows XP is now so old that it is simply not practical to support it. As its market share is so low, I will be removing stated support for XP from the download page quite soon.
XP security issues aside... rather than removing stated support for XP on the download page, perhaps mention limited support or note that not all features will work? I'm just worried that you'll follow suit like other software makers and completely cut off XP.
Such as, "The latest version of mIRC is mIRC v7.52 for Windows Vista/7/8/10 and can be downloaded through this page. Limited support for Windows XP."