404 to 301 WordPress Plugin creates cloaked adware on Search Engines

Malware can create spammy links that don’t show up on the site, only appearing when the site was visited by a search engine crawler, 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 by a high-rated popular plugin called 404 to 301, a plugin with over a 4.5 rating and over 70,000 downloads!

You can read the article here:
404 to 301 plugin with malware