Glossary
Eclipse Attack
A network-level attack where an adversary surrounds a victim node's peer connections — fed only the adversary's view of the chain, the victim can be tricked into reorgs or double-spends.
An eclipse attack manipulates a victim node's peer-to-peer connections so that all incoming and outgoing connections route through the attacker. The victim sees only the chain the attacker chooses to show, which can be a stale or alternate fork.
The attack opens the door to double-spend tricks against the victim (often a merchant accepting low-confirmation transactions), selective censorship, and selfish-mining-style coordination. Bitcoin's network hardening (Erebus-resistant peer selection, multiple connection types) has raised the cost considerably.