What's the difference between viruses and bacteria?

There
are many differences. Viruses are the smallest and simplest life form
known. They are 10 to 100 times smaller than bacteria. The biggest difference
between viruses and bacteria is that viruses must have a living host -- like a
plant or animal -- to multiply, while most bacteria can grow on non-living
surfaces.

Also,
unlike bacteria, which attack the body like soldiers mounting a battle,
viruses are guerilla fighters. They don't attack so much as infiltrate. They literally
invade human cells and turn the cell's genetic material from its normal
function to producing the virus itself.

In
addition, bacteria carry all the machinery needed for their growth and
multiplication, while viruses carry mainly information -- DNA or RNA, for
example. Viruses harness the host cell's machinery to reproduce. In a sense,
viruses are not truly "living," but are essentially information
floating around until encountering a suitable living host.