It’s a scam. They are trying to steal info from you
Try this
Double tap the home button and flick the preview for Safari off the screen.
Then go into the settings and safari and delete the history
If you sync your safari with iCloud you may wish to turn that off as well
then force your iPad to reboot by holding down the sleep and home keys for 20 seconds or so. When you see the silver apple, let go and let it reboot and hopefully that popup is gone
If you entered any info or gave anyone any information then consider that information in the hands of bad people and act accordingly.