I'm not sure about that - Mevio are definitely a real (if crappy) company that exists, they're run by Adam Curry (or were). Having said that the lack of a homepage is a little bizarre.
The other reason I don't think this is malware is that the dialogue box is the same one I get every few weeks when my login cookie for another podcast I subscribe to expires (from Giant Bomb, if that matters). The difference being, of course, that I have login details for that! The dialogue box for me seems to be appearing once an hour when itunes attempts to refresh its podcasts - I've been lucky in that I haven't had any problems with crashing yet.
Of course, it says something that it's possible to mistake itunes' normal functioning for malware...