If the site is redirecting visitors, showing content you did not publish, or triggering browser warnings, treat it as an active problem rather than waiting for a report.
At a high level: contact your hosting provider, preserve existing backups rather than overwriting them, change administrative and hosting passwords from a device you trust, and involve someone who can investigate with proper access. Then deal with the underlying cause before restoring anything.
Our malware warning-signs page covers this situation in more detail, including what to expect from a proper clean-up.
We will never ask you to send us passwords or hosting credentials to receive this review. It is done entirely from the public website.