How Does a Tampered Block Header Affect Network Security?

A tampered block header, if successfully propagated, can lead to a security breach. If the previous hash is altered, it breaks the chain's integrity.

If the Merkle Root is altered, it can hide malicious transactions. If the nonce is altered after mining, the block is invalidated.

Any successful tampering can result in a chain fork, double-spending, or transaction censorship, severely undermining the network's trust and economic value.