'Your PC Has a Trojan' Pop-Ups
A popular online tactic involves showing bogus malware warnings to users. The 'Your PC Has a Trojan' pop-ups operate in a similar manner. It tries to add legitimacy to its claims by pretending that the warnings are coming from a reputable security vendor (Norton, McAfee, etc.) and a scan has detected multiple malware threats on the user's computer. The fake scares continue with the dubious pop-up also claiming that the device has already sustained heavy damage. Users may see messages about their information being compromised, threat actors spying on their Internet activities and other similar claims.
When encountering such a scheme, it is important to remember that no website or page can perform a malware scan on its own. All of the scary-sounding statements are fake, and their only goal is to force the targeted user into downloading a promoted application that will supposedly fix this non-existent problem. Typically, the applications spread via such deceptive means are intrusive PUPs (Potentially Unwanted Programs).
In fact, the reason you are encountering the 'Your PC Has a Trojan' pop-ups in the first place could be such a PUP that has managed to sneak itself onto your computer. PUPs can perform numerous intrusive actions on the system. They can generate unwanted advertisements (adware), take over the browser's settings, and modify the homepage, new tab page, and the default search engine to open a sponsored address (browser hijackers), and even spy on the user's browsing activities.