Is the virus alert on my iPhone a scam?

It is probably a scam.

Probably? Try, absolutely a scam.

Overwhelming amount of malicious software for iPhones is not persistent, so a reboot will remove it.

Overwhelming? Name even just one piece of iOS malware that isn't a nation-state attack that costs over 1 million dollars - per phone!

You don't have any viruses on your phone, it is a scam message designed to get you to purchase unnecessary software or phish for personal information.

Read more about it here -

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

It is probably a scam.

but to be sure - restart your iPhone. ( I mean turn off completely and turn back on)

Overwhelming amount of malicious software for iPhones is not persistent, so a reboot will remove it.

Yes, it’s a scam.

It is an ad delivered to you by a website you are visiting.

It is designed to scare you into buying useless software.

Unless it came in response to manually uploading a file, yes.

(259832)

Of course it is a scam.

You should expect to see many more messages like this in the future.