There are tens of thousands of pieces of malware circulating on the Internet, including viruses, worms, Trojans, dialers and other monsters. These pose a serious threat to your security. Antivirus software can counter this malware.
You should only run one antivirus program on your computer. If you run multiple antivirus programs, they'll conflict. Make sure to keep it updated, as virus definitions are constantly being added.
Free antivirus for Windows:
Free antivirus for Mac:
Sophos Antivirus for Mac Home Edition
Avira AntiVir Personal
A firewall hides your computer from probing hackers while you're online. It also watches your computer's network traffic to watch for suspicious activity. As with antivirus software, only run one firewall program at a time or they will conflict.
Windows 7 and OS X both have decent built-in firewalls. The Windows firewall is turned on by default. To turn on the firewall in OS X, go to System Preferences>>Security & Privacy.
Free third-party firewalls:
Spyware and adware are other big threats to computer security. Spyware tracks your Web surfing and reports your interests to a computer on the Internet. Adware sits on your computer and feeds you ads. Both spyware and adware will slow your machine.
You need programs to keep spyware and adware from taking root and you need other programs to annihilate spyware and adware that collects on your computer. You should use multiple anti-spyware programs on your computer. Unlike antivirus software and firewalls, they won't conflict.
Free anti-spyware programs:
Spybot Search & Destroy
No system is entirely safe from malware. The above programs can remove most infections, but there are some infects that just won't go away. Here are some powerful last-ditch programs you can use to clean up your system.
Windows Defender Offline
Microsoft's Internet Explorer 8 and earlier is rife with security holes. IE9 is much better, but it isn't available on Windows XP. If you haven't upgraded to IE9 on Vista and 7 I strongly recommend you do so. If you want an alternative to IE on any version of Windows, here are some browsers I recommend.