I'd go so far as to say no coin can ever be considere 100% secure. Shit just happens. Maybe a vuln becomes possible through technological advance...we can never know.
That make me think that this could happen any day soon and we wouldn't even be aware
or it. We all know that a quantum computers are being in development but we don't know
from the "free media" if there is any already in existence
Therefore US or any other government could be in possession of such technology
before anybody else and could use it to destroy the crypt currencies if they becomes of a burden
to them.
It would be similar like today in BTC mining where a company that makes ASIC and other mining
hardware mines BTC with that hardware for few months and then they sell to others
this "newest technology" hardware so that they can mine further while they will have
and will keep the real newest technology for themself for a few months just enough to have advantage
over anybody else