Immunet and Panda cloud antivirus both don’t require you download virus definitions/updates manually. Immunet and Panda cloud both use the internet to protect your PC. They both run on Windows. But, with immunet you do not have to uninstall your current anti-virus to install Immunet, but with Panda you have to uninstall your current Anti-virus programs.
I like Immunet more since I can keep my current antivirus and run along immunet as well. I haven’t tried Panda, so I don’t have an opinion on it. Immunet is fast, and uses very little system resources. It is good for older computers, and low-end computers.