There are a number of articles about how to secure your network.  This article is particularly easier to understand and also targetted towards small business owners.

Top Five Small Business Internet Security Threats » Small Business Trends

Over the past two years, there have been a number of high-profile data breach cases involving major corporations. While this may give the perception that only large corporations are targeted by hackers and thieves, the reality is that hackers are increasingly targeting small businesses because they usually do not have the resources or know-how that large corporations do.