I got the "add to circle" message today (12/7/2013). It said it was sent by someone I know, but of course the number did not match. I added the number to my phone's block list and deleted the message (without clicking on the link).
I received a text today saying "Barbara sent me a message and added you to their local network on Circle. Install to view. http://circleapp.com/download?sms=2"..... of course now that I've written a complaint here, I'm deleting the text!
I got the same message wanting to add me to a circle of friends !!! I knew something was strange ,that's why did not click on the link .... Guess it is time to change my password , There has to be a sour Tomato in every store !!