I have antivirus software, so why does my PC keep getting infected with viruses and malware?
Having updated antivirus software is important, but it is only part of the solution to keeping your PC infection free. Most viruses and malware infect your PC through security holes in your software. That is why it is imperative that you install all available security updates on a regular basis.
Microsoft makes it fairly easy to install software updates. You can even configure your PC to install them automatically per the following article:
However, there is more to the story than that. Your PC is also likely filled with software from other manufacturers, and in fact most infections these days comes from security holes in Adobe Acrobat, Adobe Flash, and Sun Java software! So you will want to make sure that you also install the latest updates for those software packages in addition to updates from Microsoft.
If you are using another browser such as Mozilla Firefox, Opera, or Google Chrome, you will also want to make sure you are running the latest version. Having updated software installed will allow your antivirus software to function as it should, and help to give it a fighting chance against all of the nasty threats floating around out on the Internet.