Back when WordPress was pretty young there’s some loopholes that enable hackers to inject unauthorized and dangerous HTML code into your website pages, thus promoting the distribution of malware that damages the end users computer. I was once there and got penalized by Google for one of my sites. However, they are gentle enough to detect that this might not be my fault but still decided to bring down the overall ranking of all the pages on that site for a while to protect Internet users and notify me.
If you have spotted anything suspicious or sense that your overall site ranking is down, you may want to check it out for sure if your site has been infected with malware or anything else that’s a threat to your site and the visitors.
And Google will present you a detailed report of what they have found on your site for the last 90 days.