I've tried to get into CS:S tonight and my Steam account asked me for my password, which is unusual. I put in what I expected my password to be, but nothing. Same for any other password I was using around the time. This makes me think that whoever hacked 5punk a bit back might have got into it and changed the details, but my username is in no way related to my 5punk username. I've tried the retrieval thing both from my username and from my product code but I've not had any emails back yet.
Anyone any suggestions? Have I had my account stolen?
I've waited about half an hour and now I've emailed Steam support with a photo of the product code in the HL2 case and a post-it with my account name on it, as well as telling them which Steam purchases I've made and the likely time it was hijacked. Fingers crossed.