In case anyone is sceptical of VVV's mini rant , there are a million posts on the web that say exactly this. Here is just one that really covers it completely:
"Penicillin works by dissolving the cell walls of most bacteria. Viruses have no cell walls. They're just little (tiny even compared to a bacterium) balls of armored protein plating surrounding a package of what is usually RNA. The RNA carries instructions on how to build more viruses. When the virus bumps into a suitable cell it injects the RNA, which takes over the cell and converts it into a factory for producing more viruses.
It's not even technically "alive" because it can't do much without a host cell. No metabolism to jam, a durable capsid or envelope that looks a lot like other things in a cell you don't want to dissolve... killing viruses is hard because they're so simple there's not much to break. Their simplicity is their strength.
There are antiviral drugs but they don't work too well. Remember that antibiotics will do absolutely nothing against a virus."
That's the end of today's lecture ;-)