canarytokens.org

Canary tokens are a free, quick way to help defenders discover they’ve been breached (by having attackers announce themselves). Tokens consist of a unique identifier (which can be embedded in either HTTP URLs or in hostnames). Whenever that URL is requested, or the hostname is resolved, a person will be sent a notification email to the address tied to the token. To start to use a tool:
– select your token,
– provide an email address or webhook URL (or both),
– set a reminder note when this token is triggered.

LINK: http://canarytokens.org