Once your castle is built, you're safe, right? Not so fast. A major factor in avoiding potential threats is being careful about what you download and which sites you visit. While you know that Download.com only offers safe content, what about sites you've never visited or aren't sure about? Enter SiteAdvisor, a helpful browser add-on for Internet Explorer or Firefox that gives you inside information on sites even before you visit them. Using a color-coded system, a visual alert informs you whether a site is safe (green), requires caution (yellow), or is potentially dangerous (red). SideAdvisor also adds the color-coded warning and other site information to Google search results, so you'll be able to spot threats before they infiltrate your castle.

Read a CNET editor's review of SiteAdvisor.

While no set of software is totally bulletproof, setting up basic PC security is simple with these six programs. We highly recommend you build a functional system to guard against the potential threats outlined here. If you are vigilant with frequent updates and scans, your PC castle will be a safe place for both you and your data.