facebook is offering the opportunity to like what people are sharing, but sometimes you really don't like waht they're sharing and you would like to be able to dislike... Surfing on this need some malicious developpers have created the dislike button application. They pretend to be the facebook official dislike button but as soon as you install it you will start having issues.
They will steal your personal data including your emails' contacts and shoot some spam emails.
If you remember this button was existing last year on facebook and you were able to dislike ads on facebook as you can see on the picture below...
I guess if facebook decided to get rid of this dislike function it's because it was not positive to report to advertisers... It's always better to tell them only 5 people like your ads than 10,000 dislike it!