Yubico is a security company that provides physical authentication devices called YubiKeys, which can be used to authenticate users with two-factor authentication (2FA) for various services, including Sentry. The YubiKey acts as a physical button that can be pressed to authenticate the user's identity when plugged into a computer. This eliminates the risk of malware, phishing, and man-in-the-middle attacks by providing a direct connection between the user's device and the authentication server. Sentry has integrated with Yubico, allowing users to easily enable 2FA using their YubiKey, which supports multiple security protocols such as FIDO U2F, Secure Static Passwords, and OATH-TOTP. The integration makes it easy for users to protect themselves from online threats while enjoying the benefits of Sentry's features. As a special offer, Sentry is providing a promo code that allows customers to purchase a YubiKey and receive a second one free, making it an attractive option for those looking to enhance their security.