Hacked!
It looks like my blog got hacked. I noticed that there were some weird posts related to an essay writing service, which I've now deleted. I'm not sure of the attack vector. I had a relatively weak password for my Wordpress user, which could have been the entry point. I'll have a look at the server this weekend and see what I find. At least it's prompted me to do some work on improving the security on the server and to do some software upgrades. I need to set up the letsencrypt certificates as well.