brfag here
afaik, the e-voting down there is more or less safe (compared to the stuff that happens in the us)
consider:
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multi party: there are 3-4 major political parties, then a dozen smaller ones. I believe all of them have auditing rights to the source code and counting process
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like all sane places in the planet, you are required to provide an id to be able to vote
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Brazil is an unstable democracy. This cycle has less around 30 years. Which means the voting process is fairly new and up to date
Voter manipulation, if you will, only happens at the psychological level. See, for example, how Lula lost his bid in the early 90s (timed media scandals, iirc)
Brazil has a fuck ton of issues. Voter fraud is not one of them.