So I had an iPhone 7 for all of 2017. At some point during that time I started getting a lot of pop up ads and redirects while using the internet. They only happened when I was using a browser, but it didn't matter which browser. I tried Safari, Chrome, and Firefox and had the same issue on all of them. I would get redirected from random websites that I generally trust to an ad website, but rarely the same ads site as the last time. When the popped up I couldn't make them go away without closing the tab. It was usually either something about winning some money or that I had been hacked and needed to download some app to get rid of it (again, not usually the same apps or "prizes" were shown to me twice so I couldnt pinpoint a source). I tried a ton of stuff and blocked cookies and pop ups and cleared all my catches, then used incognito mode to browse, but still had the issue. Every malware scanning app said my phone was free from adware.
A couple weeks ago, I decided to get the Samsung s8. Everything from my iPhone was wiped except my sim card which was transferred into the Samsung. Almost immediately I started get the redirects again. I have tried everything and scanned my phone with trusted malware scanners (which said they found nothing) and tried a lot of the tips online. I have even been using browser that is supposed to block all pop up ads and tracking sites. I'm still getting them. Also, I get a lot of spam calls but I don't know if that's related or not.
Added (1). Other info that may be important:
-this happens on 4g and all wifi so it's not just my wifi
-I have never followed any of the adware links
-I only download apps from the apple app store and google play
-my phones are rarely connected to my computers (neither computer has ever had a virus to my knowledge)
-I use t mobile
Read more: https://samsungus.org/qa/s8/ad-redirects-on-both-my-iphone-and-samsung-but-no-ad.html