It wouldn’t be an election day if I didn’t remind you it’s not a secret ballot. Notice that officials record the serial number of your ballot sheet against your entry on the electoral roll so your vote can be traced. The intent of this is so an investigation can be carried out in the event of an accusation of electoral fraud.
It’s been a while since I read the letter of the law on this (and I did read the relevant act of parliament) but IIRC the protections round this are nominal. Fortunately this is one occasion that you should be thankful that the people you are electing aren’t competent enough to be using this data. (With the corollary that sufficiently advanced incompetence is indistinguishable from malice.) The one saving grace is this is currently a paper record. However, if it was stored electronically then I’m sure by now Russia would have hacked it and leaked it to whoever they thought was most likely to destabilise the country.
If you were to combine this data with profiles from both social media and advertising data brokers you would have a perfect bubble targeting campaign. Not only can you reinforce the beliefs of your own supporters but you can also use the matches on people who voted for your opponents to spread disinformation (fake news) to discredit them. (Note that the “perfection politics” of the left’s voters are particularly susceptible to this later tactic.)
This isn’t idle speculation, all the elements of this scenario have been reported recently. Hacking aside, none of this is difficult. In fact, it’s pretty much an ideal case study in current online advertising practice. Even the online marketing Twitter bots agree with me on this:
When marketing commercial tat the source data generally comes from customer databases, analytics and market sector demographics – when marketing political tat the ideal source data would be voting records which, if it were a true secret ballot, would be unavailable.
Don’t let this put you off from voting (that’s the perfection politics I mentioned earlier) but do be aware that there is plenty of credible evidence that this kind of thing is happening in world politics at the moment.