I would definitely say biological viruses are a life form. They use as a substrate. However, you need the ability to mutate in order to evolve. Computer viruses can't do that at the moment, they are dumb machines/tools that just keep doing the same thing over and over until we wipe them out.
IMO, self-replication is the most fundamental characteristic, and the ability to mutate/evolve is key as well. The rest is all details.
IMO, self-replication is the most fundamental characteristic, and the ability to mutate/evolve is key as well. The rest is all details.