I’d never updated my WordPress software since it’s installation a couple of years ago. Bad.
Bad bad bad.
Apparently, there’s now an active worm, er, worming its way around demolishing unpatched older versions. With a sense of urgency, I’ve just followed the “detailed upgrade” instructions from wordpress.com, which worked flawlessly for me. My old plugins and the changes and new code I had done for my theme worked perfectly after the upgrade. If you use WordPress for your blog and haven’t updated/upgraded in a while, now is the time!