▁the ▁operating ▁system ' s ▁capabilities ▁by ▁directly ▁patch ing ▁OS ▁calls , ▁thus ▁receiving ▁control ▁instead ▁of ▁the ▁operating ▁system ▁when ▁applications ▁( including ▁the ▁F inder ) ▁made ▁system ▁calls . ▁Gener ally , ▁once ▁an ▁extension ▁had ▁done ▁what ▁it ▁wanted , ▁it ▁was ▁supposed ▁to ▁pass ▁on ▁the ▁( poss ibly ▁modified ) ▁system ▁call ▁to ▁the ▁operating ▁system ' s ▁routine . ▁If ▁multiple ▁extensions ▁want ▁to ▁patch ▁the ▁same ▁system ▁call , ▁they ▁end ▁up ▁receiving ▁the ▁call ▁in ▁a ▁chain , ▁the ▁first ▁extension ▁in ▁line ▁passing ▁it ▁on ▁to ▁the ▁next , ▁and ▁so ▁on , ▁until ▁the ▁last ▁extension ▁passes ▁to ▁the ▁operating ▁system . ▁If ▁an ▁extension ▁does ▁not ▁hand ▁the ▁next ▁extension ▁in ▁line ▁what ▁it ▁is ▁expecting , ▁problems ▁occur ; ▁r anging ▁from ▁unexpected ▁behavior ▁to ▁full ▁system ▁crashes . ▁This ▁is ▁triggered ▁by ▁several ▁factors ▁such ▁as ▁care lessly ▁program med ▁and ▁mal icious ▁extensions ▁that ▁change ▁or ▁dis rupt s ▁the ▁way ▁part ▁of ▁the ▁system ▁software ▁works . ▁ ▁In ▁addition , ▁extensions ▁sometimes ▁competed ▁for ▁system ▁resources ▁with ▁applications , ▁util ities ▁and ▁other ▁extensions , ▁leading ▁to ▁crashes ▁and ▁general ▁inst ability . ▁Many ▁users ▁happ ily ▁loaded ▁every ▁extension ▁they ▁could ▁find ▁on ▁their ▁computer , ▁with ▁little ▁or ▁no ▁impact . ▁O thers ▁fast id iously ▁avoided ▁any ▁non - ess ential ▁extensions ▁as ▁a ▁way ▁of ▁avoid ing ▁the ▁problem . ▁O thers ▁were ▁jud icious ▁in ▁the ▁addition ▁of ▁extensions .