Just checking a few of my WordPress sites and it seemed that two were hacked into. Didn’t lose any data like other people have been reporting but working on upgrading them all.
You will notice the hack as it leaves a bunch of code in the permalinks. You can read more about it here as well as a solution. Journeyetc.com.
I discovered it as I went to make a new post and filled in the title of the post in the draft and it had a bunch of code added in the permalink structure. Just follow the instructions on the link above and hopefully all will be ok.