user129419: What if I deployed 3 of my personal tampered/hacked full nodes(with one of them a miner too) that accepts invalid blocks with proper PoW (containing invalid transactions) and rejects valid blocks. Assume there were previously 2 neutral full nodes in the blockchain with one of them a miner. Whose copy of the blockchain will be the true one now in such a case where we have majority of tampered full nodes accepting invalid blocks.
Also is this what's called a sybil attack in a blockchain?

user63872: The other two nodes would attempt to validate the invalid block, find it to contain invalid transactions, and thus those nodes will discard and ignore it.
Those two nodes will continue to follow the longest chain that is valid according to the rules they enforce. There could be one million other nodes that all follow the invalid block, but that would be without consequence to the two ('honest') network peers.

Whose copy of the blockchain will be the true one now in such a case where we have majority of tampered full nodes accepting invalid blocks

If they continue to follow the invalid chain, then the malicious nodes would create a new network, due to an incompatible (hard forking) rule change. The original network would continue to operate, otherwise unaffected by this.

129419: <p>What if I deployed 3 of my personal tampered/hacked full nodes(with one of them a miner too) that accepts invalid blocks with proper PoW (containing invalid transactions) and rejects valid blocks. Assume there were previously 2 neutral full nodes in the blockchain with one of them a miner. Whose copy of the blockchain will be the true one now in such a case where we have majority of tampered full nodes accepting invalid blocks.</p>
<p>Also is this what's called a sybil attack in a blockchain?</p>
 63872: <p>The other two nodes would attempt to validate the invalid block, find it to contain invalid transactions, and thus those nodes will discard and ignore it.</p>
<p>Those two nodes will continue to follow the longest chain that is valid according to the rules they enforce. There could be one million other nodes that all follow the invalid block, but that would be without consequence to the two ('honest') network peers.</p>
<blockquote>
<p>Whose copy of the blockchain will be the true one now in such a case where we have majority of tampered full nodes accepting invalid blocks</p>
</blockquote>
<p>If they continue to follow the invalid chain, then the malicious nodes would create a <em>new</em> network, due to an incompatible (hard forking) rule change. The original network would continue to operate, otherwise unaffected by this.</p>
