, voting is compulsory
. Or rather, turning up to your local polling place and having your name ticked off is compulsory - what you do after that, in the privacy of the voting booth
, is up to you.
This distinction has led to the emergence of a phenomenon known as the donkey vote. In marked contrast to the US and UK, upon which our system of government is based, Australia uses a system in which the voter ranks the candidates 1, 2, 3 etc in order of preference. A donkey voter is someone who, apathetic or angry at being forced to vote, simply ranks the candidates in the order in which they appear on the ballot paper.
It is estimated that up to 5% of voters choose to express themselves in this manner, hence donkey votes can determine the outcome of particularly close elections. Of course, donkey votes must be counted since the ballot has been filled in correctly and it is possible that the voter did indeed prefer the candidates in that order. In the past, candidates were listed in alphabetical order and there are several known cases of candidates being chosen to represent a party primarily because their surname began with the letter A. Nowadays they are listed randomly.
It would, it seems to me, make more sense and take less effort for these fools to simply leave their ballot blank - after all, they're anonymous.
See also informal vote; spoiling your vote.