These days, one of the greatest threats to your PC is that of so-called poisoned Web pages, which contain malicious downloads, or that may do damage to your PC all by themselves. Anti-spyware and anti-virus software may not protect you against these pages. If you're looking for an extra layer of protection against them, the free AVG LinkScanner is a good bet.
AVG LinkScanner sits in the background and protects you in several different ways with its Search-Shield and Active Surf-Shield technologies. Search-Shield works when you search on Google, Yahoo, and other search sites, telling you for every search result whether it's safe to visit or not by placing a small colored icon next to each result. To find out details about potential dangers for flagged pages, click the icon and you'll get more information.
Active Surf-Shield scans the Web page behind every link that you click when you browse the Web. If it finds that the site is dangerous, it will stop you from visiting the site and let you know it's done so.
The program also gives you the option of installing the AVG Security Toolbar, which gives you easy access to turning Active Surf-Shield and Search-Shield on and off. It doesn't appear to do anything else, though, and it also includes a Yahoo search box. I found it of no use, so you might want to consider whether to install it. AVG LinkScanner works fine without it.