Keep your computer up to date with the latest and best in software!
The software that needs to be updated most often is the definition files for your anti-virus and anti-spyware packages. These updates contain the latest list of viruses and other malicious software and can often be updated several times a day.
Next on the list of things to update is the operating system, (e.g. Windows, Mac OS, Linux,) every computer has to have an operating system so this is the first place hackers look at for a way in.
The order in which you update the rest of your software depends on how popular it is. Hackers will attack the most popular software first as it is more likely you will have it on your computer.