A validator is a node in a proof-of-stake blockchain that helps secure the network by proposing new blocks or attesting to blocks proposed by others. Instead of mining, validators lock stake and use signed messages to show they are following protocol rules. Their software usually handles key management, uptime, networking, and block-signing duties.
Validators matter because they sit on the trust boundary between blockchain consensus and the systems that operate them. If an attacker compromises the infrastructure behind a validator, they may steal signing keys, redirect rewards, disrupt service, or trigger slashing if the node behaves incorrectly. Defenders protect validators with strong access control, hardware security modules or isolated key storage, monitoring, and rapid containment steps such as removing a suspected node from duty. In incidents, taking a validator offline can reduce further risk while investigators check whether only operations were affected or whether keys and funds were exposed.