how about: create a website with a random string in the URL, send that URL via whatsapp combined with content that likely triggers many safety bells (at facebook, whatsapp, nsa,...) to a contact, and make sure that contact does not open the URL. create a second website (same domain) with a different URL, also with a random string, and use this to compare. check if first URL gets a hit, and if yes, check if second URL gets same hit. (spoiler alert: first URL will get a hit, second won't ;-D)