Malware “Trojan virus” pop up

Today on Safari, I recieved an alert saying that “iOS 12 shield“ detected a Trojan virus on my iphone, and that I needed to contact Apple for it. It seemed pretty legit, but I didn’t fall for it, and I closed the tab and app. I’d just like to know if iOS 12 is such a thing, and if my alert could’ve been legitimate?