First, never open any e-mail attachment that comes from a source you don’t know or trust. Second, keep antivirus software installed on your computer, updated, and run regular system scans. Third, install updates to your operating system as soon as they are released. These updates often include patches to fix vulnerabilities. Fourth, use a firewall; there’s one built into modern versions of most operating systems, just make sure it’s activated. Fifth, if you do encounter a problem, run multiple antivirus program scans to ensure the infection is cleaned up, and consider reinstalling your operating system to remove every trace of malware.