Blacklists and shared salary databases. If you move from one big tech company to another, your new employer typically knows exactly what you make, because that

Blacklists and shared salary databases. If you move from one big tech company to another, your new employer typically knows exactly what you make, because that data is often shared. Some HR departments will also (although it's never put in writing, for obvious reasons) assist future employers in finding back-channel references. This is a very old game, and the original reason for employers to share all that data was to blacklist "troublemakers" who might unionize the workforce. Now, it's more often used to verify compensation (lest people lie and big themselves up) and enforce no-poach pacts, but it's every bit as unethical.