The next time the browser is opened, do not restore the previous session, otherwise you will end up reopening the malicious site/s. In these cases, terminate the browser using Task Manager or simply reboot the system. The "Your Mac Is Infected With 3 Viruses" error can be removed simply by closing the web browser, however, some rogue sites employ scripts that prevent users from closing browsing tabs/windows.
If you have already done so, delete it immediately and certainly do not purchase any full version. This error is fake and you should never download any promoted software. Therefore, users are encouraged to purchase the 'full version'. Furthermore, 'free versions' of these apps are supposedly incapable of removing the listed infections. Users are encouraged to download software that will 'remove' allegedly existing viruses, however, these applications are typically designed to display long lists of infections that do not exist. Cyber criminals employ this scam model to proliferate fake system optimization/anti-virus tools. Be aware, however, that this is a scam - "Your Mac Is Infected With 3 Viruses" error is fake.
This error states that the computer is infected with a number of viruses and encourages users to immediately scan the system. Research shows that potentially unwanted programs typically infiltrate the system without permission and, as well as causing redirects, deliver intrusive advertisements and gather sensitive information.
"Your Mac Is Infected With 3 Viruses" is a fake error message similar to Please Call Apple Support, Bankworm Virus, We Have Detected A Trojan Virus, and many others. It is displayed by malicious sites that users often visit inadvertently (they are redirected by potentially unwanted programs or intrusive advertisements delivered by other deceptive sites). What is Your Mac Is Infected With 3 Viruses?