Mr Brodie said he had alerted the party and waited until the problem had been fixed before going public via his blog. National's HQ had moved "pretty quickly", contacting him on Thursday to say the problem had been fixed. A security flaw he had pointed out earlier had also been fixed.
The "hobby hacker" had started looking into political party website security, intending to start a non-partisan conversation about web security, before the Dirty Politics revelations emerged.
In the week between his discovery and the fix, Mr Brodie said he had winced every time he heard Mr Key make a statement about Labour leaving its website open.
National Party secretary Greg Hamilton confirmed a tech blogger had identified a minor issue with the party's membership website. The party had thanked him for his advice and fixed the issue.
Mr Brodie also found serious flaws on the Conservative Party's website allowing access to anything on the party's server, "which is basically game over as far as their security goes". He had alerted the party before writing in his blog.
"Hopefully it's becoming increasingly clear that political parties need to be aware of threats not only to their website security and member privacy, but to their reputation as being managers capable of running a tight ship.
"I'm not expecting our leaders or their campaign staff to be able to fix this s*** themselves, but I am expecting those in charge to be identifying areas where their knowledge is lacking, delegating to better qualified people and getting assurance that their bases are covered."
He was not a professional security tester, merely "some random guy ... who stumbles across these things".