Internet security - the basics

Antivirus software… Use it and keep it up to date! 

Use a firewall – Windows has a firewall built in and most antivirus packages also include one. 

Keep your system up to date  - Not just anti-virus and firewall software, but the system in general.  Developers regularly issue updates/patches/fixes. These updates could be released because the developer has discovered a security weakness in their product and should not be ignored. If you are prompted to download an update then you should!