Interesting debate for sure... some people claim they are more secure because you have an extra layer of monitoring and control. Added layers (the virtual layer) can give you more options to monitor trafic flows throught the virtual interfaces. It also makes it harder for viruses to detect they are being blocked by the virtual layer.

At the same time, virtual layers, we can assume will slowly become vulnerable to viruses and such, and then could leave you less secure, due to the access to many OS's from one centralized location.

So I think both cases can be made, however there are very few if any actual published viruses for the hypervisors on the market, so I would lean toward the practicle current answer being they are in fact, more secure. =). Of course I could make a different question that breaks this into more specific questions.

Thanks for the comment, I will take it inot account when I publish a new set of questions.