Premium plugins are especially popular when they help blogs make money: eCommerce, SEO, affiliate and customer management. Not many webmasters are ready to pay for plugins, especially when they can find free or nulled versions of the same plugins on the Internet. In this post, well talk about patched malicious premium plugins. We’ll talk about what they do, how they work, and about websites that build their businesses around stolen themes and plugins.”]
Source: https://blog.sucuri.net/2014/03/unmasking-free-premium-wordpress-plugins.html