You should be. It's not something to be paranoid about. Many hackers look for small, relatively unknown companies with little of interest in their computer files. Maybe they're new to the hacking game and want to test out newly acquired skills. Maybe they want to use your systems as a launching pad for other larger attacks.
Some hackers peddle their wares by planting viruses.
Read this tutorial to learn about different types of viruses, who's vulnerable, and what you can do to protect yourself and your network. If your company is in the business of e-commerce, there are extra security measures you need to consider. Many small businesses use a hosting service to handle their sites. If you do, make sure you consider these questions before you sign on the dotted line. All this, plus how to protect yourself from being attacked by one.