There are plenty of Anti-Virus programs available for Windows, so it can be hard to know what program to choose. We recommend reading test results such as those provided by the organizations below to determine what software fits your needs.
AV-Comparatives website: "Independent Tests of Anti-Virus Software"
AV-TEST website: "The Independent IT-Security Institute"
Below are a few examples of software to help protect your computer from viruses, spyware, and malware. Most have free as well as paid versions. You should not have more than 1 Anti-Virus program installed at a time or they may conflict with each other and cause problems on your computer. You should have 1 Anti-Virus program and at least 1 Anti-Spyware & Anti-Malware program.
Programs should be configured to run scans on a schedule so that you do not forget to scan.