Why did Social Security deposit extra money into my acct on Oct. 5, 2016? Did everyone receive extra money?
I haven't heard of any special payments going out, but this is normally the time of year that Social Security processes automated benefit adjustments. So, the payment you received could be back pay due as a result of a retroactive rate adjustment for any of a variety of reasons (e.g. delayed retirement credits, additional earnings, etc.).
Direct deposits are often received up to a week or more in advance of the explanatory notices that Social Security sends in the mail, so I would wait a while to see if you receive an explanation. If you don't, you should probably check with Social Security.