Is there no 3rd option?
It could be cryptographically secure but not scale, for example? Or a problem with the implementation?
The cost of attacking/spamming an IOTA network is virtually $zero, and even f you cant change the past you could perhaps delay the future, indefinitely? Or am I mistaken?
No details are available now.
Very well.
Last Q:
Is the tangle only as fast as its slowest moving part?
i.e. is it enough for an attacker to take down only part of the network (<51%) to effectively make the network useless?