If you suspect your Booking.com account has been compromised, you must act immediately to secure your personal data and financial information. First, attempt to log in and change your password to something unique and complex; if you cannot log in, use the "Forgot Password" feature. Simultaneously, contact Booking.com customer service through their official help center to report the breach so they can freeze any suspicious activity or unauthorized bookings. Crucially, check your linked payment methods and contact your bank or credit card issuer to report potential fraud and, if necessary, cancel your cards. Scammers often use hacked accounts to send fraudulent messages to customers claiming they need to "re-verify" payment details through external links; never click these links, as Booking.com will never ask for payment outside their secure platform. Review your recent "Bookings" list to see if any unauthorized trips have been scheduled. Finally, enable Two-Factor Authentication (2FA) in your account settings once you regain access to add an extra layer of security, and ensure the email address associated with your account is also secured with a strong password, as hackers often target the email first to bypass account security.