Depending on how much damage the virus caused and how widespread it got, I'd say a minimum of 3-5 years and a fine, which probably would never be collected.

If the virus caused millions in damages or losses then a longer sentence would be justified.

Since these are not crimes that kill or cause physical harm to people, however, I'd tend to believe that if someone were actually convicted for writing or spreading a computer virus, they'd spend less than 18 months in Club Fed with internett access!