Remove malware code injection on WordPress

My WordPress site is not working properly. There is some kind of malware that is injecting code and links into all pages and blog posts. I need someone to find the cause, remove it and protect the site to prevent this from happening. Take a look at the two screenshots. One shows the link injected on the homepage (it happens on all pages and blog posts), and the second is the popup I get when the link is pressed. Site is set-and-forget.com Can you help me remove it?