▁e - mail ▁topology ▁( like ▁a ▁ma iling ▁list ), ▁in ▁which ▁some ▁server ▁is ▁to ▁send ▁an ▁enorm ous ▁amount ▁of ▁legit imate ▁e - mail s , ▁and ▁bot net s ▁or ▁cluster ▁far ms ▁with ▁which ▁sp amm ers ▁can ▁increase ▁their ▁processing ▁power ▁enorm ously . ▁ ▁Most ▁of ▁these ▁issues ▁may ▁be ▁addressed . ▁E . g ., ▁bot net s ▁may ▁exp ire ▁faster ▁because ▁users ▁notice ▁the ▁high ▁CPU ▁load ▁and ▁take ▁counter - me asures , ▁and ▁ma iling ▁list ▁servers ▁can ▁be ▁registered ▁in ▁white ▁lists ▁on ▁the ▁subscri bers ' ▁hosts ▁and ▁thus ▁be ▁rel ieved ▁from ▁the ▁hash c ash ▁challeng es . ▁But ▁they ▁represent ▁serious ▁obst acles ▁to ▁hash c ash ▁deployment ▁that ▁remain ▁to ▁be ▁addressed . ▁ ▁Another ▁project ed ▁problem ▁is ▁that ▁computers ▁continue ▁to ▁get ▁faster ▁according ▁to ▁Moore ' s ▁law . ▁So ▁the ▁difficulty ▁of ▁the ▁calculations ▁required ▁must ▁be ▁increased ▁over ▁time . ▁However , ▁developing ▁countries ▁can ▁be ▁expected ▁to ▁use ▁older ▁hardware , ▁which ▁means ▁that ▁they ▁will ▁find ▁it ▁increasing ly ▁difficult ▁to ▁particip ate ▁in ▁the ▁e - mail ▁system . ▁This ▁also ▁applies ▁to ▁lower - in come ▁individuals ▁in ▁developed ▁countries ▁who ▁cannot ▁afford ▁the ▁latest ▁hardware . ▁ ▁Like ▁hash c ash , ▁crypt oc urr encies ▁use ▁a ▁hash ▁function ▁as ▁their ▁proof - of - work ▁system . ▁The ▁rise ▁of ▁crypt oc urrency ▁has ▁created ▁a ▁demand ▁for ▁AS IC - based