Now this one was a new one to me, so I read this page with attentiveness. It seems that the malware can create text that doesn’t show up on the site, only on the search engine preview, which hurts your SEO and can get your site completely blocked from the search engine (Google, Bing) if you don’t get it removed. The malware is inserted with a high-rated popular plugin called 404 to 301, a plugin with over a 4.6 rating and over 70,000 downloads! You can read the entire article and the technical stuff here if you want: 404 to 301 plugin with malware . If you use this plugin, you should remove it for now, or see if they update it and fix it.