Readme.html renamed – hacked??

On a few of my sites, the readme.html in the root directory has been renamed like the following:
readme-kv489ugskgk429urgjfksjmgbt293.html or similiar. I thought it might have been a hacking attempt as I’d not updated my Visual Composer plugins since the vulnerabilities were identified. But it’s also happened in other sites without VC.

On the recent ones, the only change in the file contents is the version number.

Have I been hacked or is this a new WordPress thing??

Thanks in advance,
Toby