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A single malicious actor buying up enough tokens to take control of the chain is always a risk for DPoS. The more tokens one actor tries to buy though, the more expensive it will get. This would likely be a very expensive attack to make.

Why would you consider them malicious and why would that be considered an attack? Maybe they just wanted to buy up the coins and promote the project.

They already demonstrated on the Steem chain that they were.

If I have the kind of cheese Sun's has I will attempt to buy up enough hive and mount up stock puppet as witness

I would love to watch this movies ☺

Lol. Unlikely