Once a new way of exploiting or hacking WordPress is discovered, hackers are quick to scale up their activities across the many WordPress sites that might not yet have taken measures to address that weakness.
Why do people hack WordPress websites?
Sites are hacked for a variety of reasons. Besides the obvious reason of causing wilful damage, WordPress is often hacked by spammers looking to use your site to help them rank spammy pages in Google.
This is done by injecting links into your site, linking back to spammy pages.