Updates And Patches
From time to time, vulnerabilities are discovered in programs running on your PC. These weaknesses are regularly exploited by virus writers and hackers to gain unauthorized access to those PC's that have not been patched.
Microsoft users can visit: http://windowsupdate.microsoft.com which can automatically check what is required for both operating system and browser and then download it at your request.
Anti Virus Software
You may already be using anti-virus software but to be effective, the software should be updated on a regular basis with the latest virus definition files.
There are many effective programs to choose from, but the most common commercial products include McAfee, Symantec (Norton) and Sophos.
You can download free virus scanners from www.symantec.com or http://housecall.trendmicro.com/
A personal firewall is another program that helps protect your computer from outsiders on the Internet. When installed, it stops unauthorized traffic to and from your PC.
There are many effective programs to choose from. Common commercial examples include Zone Labs, www.symantec.com and Computer Associates.
The leading free firewall is "Zone Alarm" from Zone Labs and there are many others to choose from. Zone Alarm is now used on over 20,000,000 PCs and has been awarded the PC World 2003 "World Class Award" for Best Firewall.