Soooo... Is it a security breach or a cache error now? With Steam, I mean. It looks like a cache error, but seeing as the internet is going batshit crazy...
Just, get off steam, unlink paypal and credit card deets if you can outside of steam. The cause is unknown now so it's a ll speculation, so caution is a good thing
I'm not affected too badly, tbh. It's been years since I last used Steam, plus I don't have any Paypal or credit card details on it. I'm just interested in the issue.