▁vie wer ▁moves ▁the ▁browser ▁window ▁so ▁the ▁ad ▁is ▁outside ▁the ▁display ▁screen ▁area ; ▁ 1 2 . ▁The ▁vie wer ▁has ▁multiple ▁home ▁pages ▁set ▁so ▁when ▁the ▁browser ▁is ▁opened , ▁two ▁pages ▁open ▁in ▁two ▁tabs , ▁and ▁an ▁ad ▁res ides ▁on ▁the ▁tab ▁that ▁is ▁not ▁in ▁focus ; ▁ 1 3 . ▁In ▁the ▁case ▁of ▁pre - roll ▁video ▁and ▁video ▁advert ising , ▁if ▁the ▁vie wer ▁minim izes ▁the ▁browser , ▁tabs ▁away ▁from , ▁or ▁opens ▁another ▁application ▁over ▁the ▁video ▁while ▁the ▁advert is ement ▁is ▁playing ▁or ▁moves ▁the ▁browser ▁window ▁so ▁the ▁video ▁is ▁outside ▁the ▁display ▁screen ▁area ; ▁ ▁Re asons ▁why ▁an ▁impression ▁may ▁not ▁appear ▁to ▁a ▁vie wer ▁associated ▁with ▁fra ud ▁overcome : ▁▁ 1 5 . ▁The ▁request ▁was ▁made ▁by ▁an ▁( in visible ▁to ▁the ▁vie wer ) ▁web ▁page ▁re - direct ; ▁ 1 6 . ▁The ▁web ▁publish er ▁places ▁multiple ▁ad ▁displays ▁in ▁layers ▁over ▁each ▁other . ▁The ▁vie wer ▁then ▁sees ▁one ▁ad , ▁but ▁impress ions ▁are ▁reported ▁for ▁all ▁layer ed ▁ad s ; ▁ 1 7 . ▁The ▁web ▁publish er ▁places ▁an ▁image ▁or ▁shape ▁on ▁a ▁layer ▁over la pping ▁an ▁ad ; ▁ 1 8 . ▁An ▁ad ▁or ▁be acon ▁delivered ▁in ▁an ▁invisible ▁width =" 0 " ▁height =" 0 " ▁If rame ; ▁ 1 9 . ▁M util ated ▁( http ▁poison ing