It's a Scam. You do not have anything to worry about unless your provided personal details or password credentials by clicking the Report Now button. These warning will come up more frequently while visiting less reputable sites. This scare tactic is used to get you to download some nefarious anti virus software claiming to fix all your problems or get you to provide them personal info. They would love to have your bank account info or even your Apple ID and password.
Unless your iPhone is jailbroken, software cannot be installed over a website and you are safe to ignore it and move on.