[xaqfox]

Residential proxies are too prevalent for IP address limits to work effectively.

[nicce]

Is there some public research that how often, for example, people download malware that allows this?

[HarHarVeryFunny]

You can use cookies to track usage history

[TOMDM]

I can delete cookies to obscure usage history

[HarHarVeryFunny]

You can combine it with user PC fingerprinting

[dgellow]

You can also just ask for a login…

[HarHarVeryFunny]

You could also make the wannabe user buy a $500 retinal scanner and use biometric ID ...