VERY bad or intrusive ads.
Usually lists like
1. am i pregnant
test
2. senior dating site
3. dating site free
4. other shit
idk but probably porn
another type is clickbait ads
"you cant believe why i put this in my toilet"
and then it tells u to buy some shit
the other one is porn-like ads
these mix with clickbait ads as they are not porn, just viruses probably.