Wordfence just alerted me on this:
Alert generated at Thursday 10th of March 2016 at 02:52:39 PM
Critical Problems:
* File contains suspected malware URL: /home/mysite/www/wp-content/plugins/wordpress-seo-premium/changelog.txt
* File contains suspected malware URL: /home/mysite/www/wp-content/upgrade/MTQ2MjY5MzkwMjpmNzQ1NmI2Zjk0ZTQ2MzQ1NWM0NzRhM2IzOWZkMmNkYjoxMDUyNDM6Y2RiMWJmNmIxMjY2ZDBiNzJjNmFjNjhkMWZmYzllYTA6aHR0cHNALy93d3cubm9yZGljZ3JlZW4uc2U-M5HAdr/wordpress-seo-premium/changelog.txt
Yoast version: 3.1.1
Probably nothing.
Johan