Seems like cnet decided to start prefixing their downloads... I assume they have a license agreement which allows them to name the exe file download whatever they want
Looks more or less fine to me. You can verify by comparing the md5 hashes (you can get the mirc719.exe file from mirror sites
Highly unlikely possibility: your DNS was jacked and a really good cnet spoof site is giving you a faked mIRC installer. Again, *very* unlikely.