If there is no alt tag, search engine doesn't understand anything from the image.That's why you should use alt tag on your all pictures, which you use in your website.
Your website address or its sub-links called deep link.
He then makes you click on a series of check boxes, enter your personal details and then pass the message on to a series of friends to become eligible to the offer.
The message on the page further mentions that after you have finished inviting 15 friends you will find that the Whats App colour will turn blue (from green) when the service is activated.
Lastly, he also made you swift through some pages and download a few apps which could be a bonus for him if they too contain a malware.
A similar fake message about enabling Whats App Calling was doing its rounds recently.