The results you're seeing are probably spam designed to install a virus on your computer or trick you into visiting a website. Spammers sometimes label files with the wrong extension so you'll think they're harmless and download them, but the file is actually of a different and more dangerous type than the extension indicates.

Luckily it seems your system has detected that the extension doesn't match the file type and is refusing to open the mislabelled file.

If you right-click on the file and look it up with Bitzi, you might find that someone else has already reported it as mislabelled or harmful.