I wonder what they consider "unusual activity?" I frequently jump from toon to toon on both my accounts and haven't - yet - seen this message. Could it have to do with logging in from different locations? There can be good reasons for doing that, also. One of my guildies got this, and DBG told him he wasn't himself. He was NOT amused. When he was finally able to log back in, he was experiencing more lag than usual, and that did not help his mood, either. Although I have a cell phone, I definitely agree DBG needs to give a choice of different authentication methods.
I've never had to provide my cellphone number to authenticate any other game I play, nor has my account been hacked. All sites (not all!) I use that ask for one, also provide a way to skip it (at your own risk) or provide an alternate method. The problem is compounded by the current lack of customer service options.
The little town I live in doesn't get cell reception, so I rely on a landline as well. Requiring a mobile number would just get the game uninstalled. Email validation is still a good choice for authentication. Had some jagoff in the Philippines try to login my Steam account a couple weeks back, Steam shut him out and emailed me to let me know. Changed my password and all good to go. Edit: this is also why I do not keep billing info in any game accounts and do not keep any "cash" in my Steam wallet. If you pay for a game, make your payment and then DELETE YOUR PAYMENT INFO.
they locked me out for unusual activity last winter... for buying cash and items from the market during a discount, it's as easy as that. since it was feb, i had to get into a 4 wheel drive and go out to try and find a cell signal to get my account back, I'm never doing that again, in the middle of winter on the great lakes(lake huron) for a game. no one should have to do it if we don't have cell or very little cell service. i looked at your google voice alph, yeah umm nope, it doesn't support areas like mine.
Checked my main account and it seems to be ok, I guess I'll check my other one. Is it possible that the folks that are doing this had a yahoo mail account? There was a huge hack job on yahoo mail accounts. My second account is ok as well.
I want to thank everyone for their support. I will not have to use the 2-factor verification. There was a false positive for suspicious krono trades that CS cleared.