Can a pen-drive is safe free from virous when is top cover is lost? Pl answer.

Yes a virus is a computer program which replicate and distributes itself on a host computer- like a biological virus. Computer virus - Wikipedia, the free encyclopedia

Unlike a biological virus however it cannot be transmitted through the air. You would need to plug the pen drive into an infected computer.

I think without the lid they are a little more prone to damage (and therefore loss of your data)but I have two without lids and they seem fine.

If you are worried about viruses invest in some anti virus software like Norton.

Yes it is free and safe.