Should I be concerned about a "Critical Threat" on my iPhone?

In addition to the above…

If a website could scan your device, the scammers would upload all your data directly and not bother with this subterfuge.

Malware scans are deeply intrusive, and that access is exactly what malware would want to have, too.

In this case, this is an advertisement. Very likely an advertisement for a commercial first-few-hops VPN product.

Commercial first-few-hops VPNs badly solve a problem that hasn’t existed for a decade or so, but badly solve it in a way perfect for personally-identified metadata collection.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Assume most anything you read that’s referring to “virus” or “hacker” should be assumed to be an advertisement or scam or entertainment-related writing, until proven otherwise.

App store apps cannot scan the contents of your iPhone, because of the built-in anti-malware defenses. They can scan your network traffic though, which is what sketchy apps do to collect your metadata and other information.

It is indeed a scam. Close the offending page and avoid sites that are involved in such bogus advertising tactics.

Phony "tech support" / "ransomware" popup… - Apple Community

1267_B wrote:

How can it be proven to be a virus?

How can what be proven to be a virus?

Note: The following differentiates “virus” from “malware”, and from “adware”, and from apps badly solving problems you don’t have.

Viruses basically don't exist for iPhone.

And proving a negative is exceedingly difficult. If not impossible; that there is no malware.

There is a little malware around targeting iPhone, but that’s been very rare and targeted based on all available information. The exploits involved in that malware is usually worth multiple millions of dollars, too. Not cheap stuff, and those with it aren’t inclined to cast a wide net as they’d rather not have their expensive exploits detected and fixed.

That expensive malware and espionage tooling also doesn’t pop up a “buy this janky app” suggestions. Adverts do that.

If you’re a political activist, dissident m senior in government or private, with access to sensitive or classified data, or otherwise been an annoyance to somebody exceedingly rich, yes, the calculations here can shift.

But in recent times, viruses are exceedingly rare on any platform. But sketchy advertisements are endemic.

Some more tech ical info: Apple Platform Security - Apple Support