I do not think we as regular user will know how that virus work and how can they reach our wallets. But as far as I know, when we download a file, that can contain a virus and when we execute that file, it will infect our devices and that will depend on the source code in the virus. If the virus has a command to execute or access the wallet, the virus will try to penetrate our devices and start to do something that the creator wants. So we must be careful when we download a file from the internet.