Captcha-smart.top is a dubious website designed to deliver questionable content to its visitors. In addition, it also may employ misleading alert or warning messages that try to trick users into subscribing to the site's push notification services. It should be noted that Captcha-smart.top is in no way a unique occurrence. In fact, the opposite is true, as more and more hoax pages using the same tactics are put on the Internet daily.
The exact behavior of the site is determined by the IP address of the user. The page scans it to find out the visitor's geolocation. Then, Captcha-smart.top can decide whether to show content on its own or cause a redirect/pop-up to another site that in most cases is equally shady.
At the same time, users may be presented with fake CAPTCHA messages. The site could pretend to be conducting such a check by showing an image of a robot accompanied by a message similar to:
'Click Allow to confirm you are not a robot!'
If the users click the button as instructed, they would be granting the page the needed browser permissions to now run an intrusive advertising campaign. The advertisements could employ similar clickbait tactics and can even appear when the affected browser has been shut down completely.
To stop Captcha-smart.top from interfering with your browsing experience, you will have to revoke its permissions via your browser's 'Permissions' or 'Notifications' menu.