There is a website at crash safari dot com that will do just that: crash safari. iPhones and iPads may freeze and reboot if someone goes to that site. The good news is that more and more users are starting to realize that bad things can happen just by visiting a website. The more users become aware, the more secure their behavior will be. Known as a drive-by-download, content on webpages can cause big problems with cyber-security.
If you are an apple user, be sure to download the latest software update for your iPhone and iPad. You can click the settings icon that looks like a gear, and see the option near the top right-hand side of the screen that is labeled software update.