Well i do not belong to the science field, but i think virus is more dangerous than bacteria. Virus requires an host to survive and the virus when multiplied, can never be completely removed but can be controlled.
Hence when you catch a flu which is caused by virus, you take medicines not to remove it completely but to control it. Virus is always present in our body, but when the conditions become desirable to them, it leads to diseases etc. I think that is the basic feature of a virus.

Both bacteria and virus cause disease
Bacteria is like a living cell..it has got organelles similar to a cell..in specific terms its called prokaryotic cell..but in case of virus,we cant say its either living or non-living.As Anusha said..virus require a host..and when it is inside the host it appears to be living..outside it is just like a non-living particle..because of this feature only, virus is considered to be a transition between living and non living in Evolution.

One more interesting fact i would like to share..
We all know about Human Immunodeficiency Virus or HIV..This virus suppress our immune system, so that next time you get even a common cold,your body cannot fight against it and may turn fatal.
So what the virus do?
There is a cell called Helper T cell...This cell must be present for any immune response to take place..After its action only immune response to any foreign material will start..So what happens is that,this HIV will infect these Helper T cells..and start destroying it..Not only that...This virus will use all the machinery of the host cell and start to produce the copy of its own..thus from one infected Helper T cell, many more virus will be produced..literally the cell will become a virus factory..Thus more and more helper T cell gets infected and our immune system get weakened.
this is the basic working of a HIV virus

Bacteria ia living body very tiny that cannot be seen with naked eyes. all bacteria are not harmful. There are many bacteria in our body. In some diseases the friendly bacteria are inserted via injection to fight with the harmful bacteria. The curd contains friendly bacteria. Virus is on theother hand harmful substance, not necessarily living body. -

Yes..as gulshan said..some bacteria are very useful to us..
There is group of bacteria called E-coli living inside our body..it produce Vitamin K for us..This is the reason why doctor prescribe Vitamin tablets when you eat antibiotics, because the antibiotics will kill this useful bacteria also!