Thanks guys. That's the weird thing: I have mobile two-factor enabled but that seems to have done nothing.
I know exactly what happened the first time (I got the same Steam transmitted disease DM you all got from me) but I've seen nothing of the sort since then and had already reset all my logins. So, whichever hackers had access to my account originally shouldn't have been able to reaccess today. But here we are.
Ideally Steam Guard will prevent there from being a third time but we'll see.

Same, hadn't been DMd by anyone. Steam Guard is free btw, just download the Steam app on your phone and connect your account, before someone else does.

Sorry to hear that, hope you get it sorted out! I haven't gotten any DMs fortunately. Do you have Steam Guard enabled? It'd be pretty worrying if this happened despite that.

Hey, so, my account got hacked again. If you get weird DMs from me that aren't in proper English and call you "bro" it isn't me. I virtually never use Steam DMs so if you start getting them from me be suspicious.
The hacker blocked everyone I warned, so if you get a friend add from this account now, that's me trying to add you back.

sorry man im gonna remove you from friend cause the bot keeps spamming me, you can re-add me when you got your account back ofcourse! good luck and sorry for you

+1 on @weirdphil

It's trying to phish account information. Get 2FA setup and change your creds please!!! It's actually really hard to tell if it's a scam because of how genuine it feels. If I hadn't read about it, I'd have fallen for it.

Don't want any damage done to your account, as you've invested so much into it.