IIRC this spam attack cost the attacker only $5000 but rendered the network pretty much useless for hours
https://en.m.wikipedia.org/wiki/Hashcash
Having users to pay actions make spam unprofitable, as spam relies on tragedy of commons and abusing public goods. This is why there is so much less SMS spam compared to email spam.
IIRC this spam attack cost the attacker only $5000 but rendered the network pretty much useless for hours