It is quite simple. The first thing you should be concerned about for your computer, whether you’re buying a new one or reinstalling the operating system, is installing some form of anti-virus software. As part of the protection and security of your system (along with, for instance, a firewall), anti-virus software is the most important aspect for your system’s safety.
Anti-virus software protects your system against a wide range of threats, including – of course – viruses. A virus such as a Trojan Horse, for instance, could easily damage your system to the point that you would need to reinstall the operating system and start from scratch. Obviously you don’t want to lose all of your data (which would be infected; lost if you hadn’t backed up your files), so this gives just a slight picture into the importance of anti-virus software.
So exactly what anti-virus software do you choose – and how much will this cost? Answering the latter question first (and ignoring the former in regard to specifics!), there is no need to spend money on anti-virus software. There are a number of very good anti-virus programs that are free, make no mistake. This is the development of technology; a decade or two ago and you would need to pay for something halfway decent.
In your search of anti-virus software, make sure it is well-respected. It should offer regular updates to keep up with the viruses that are discovered on a regular basis (compare to advancements in processors) and protect your system with e-mail, downloads, and other manners.
Once you decide on a program make sure you stay up-to-date with the latest patches and updates. Run scans of your entire system on a regular basis, perhaps once a month or two, to ensure your system is protected. You should also backup all important files to ensure your systems are safe against viruses.