Macs are notoriously virus proof. Unfortunately, the reputation has given millions of Mac owners a false sense of security. Macs rarely get viruses because most malware lurking about the Internet is geared towards the Windows Operating System, and Macs are built upon the solid UNIX core. However, Macs occasionally fall victim to a computer virus. If you suspect you may be affected by a virus, perform a scan.
Purchase antivirus software such as McAfee VirusScan for Mac. This software costs money but does a great job of detecting viruses on Macs. The software can be downloaded onto your computer where you can use it to run a virus scan. Some programs operate in a passive mode that allows them to detect viruses without the need for a scan run.
For those who don't want to pay the price, download free antivirus software such as ClamXav. Though not as sophisticated as the priced antivirus software, the ClamXav does a great job for a zero-cost product.
To avoid a virus, do not download software from unaccredited or lesser known sites. Adult sites, free movie or television sites and others that entice you to download something are possible risks. Use a hardware firewall in your router or activate the Mac firewall in the Security section of System Preferences. Sometimes getting hit with a virus is unavoidable; malware writers are sneaky and smart.