WP Menu links hacked

Somehow a WordPress site I am managing has been hacked by a pill selling company in Russia. When you click any menu link, it takes you to a supposed pharmacy site that sells pills. I am checking with WP the hosting site and the Domain registrar, but I thought I would also check here to see if anyone has some suggestions. I have searched the entire WP site for any file containing the URL it is redirecting to ([ link removed ]) but as I had already guessed the URL did not show up. I also checked the MySQL database WP uses but didn’t see any reference there either. Has anyone else had experience with this type of nightmare?