I have several questions as I am about to go through a TS/SCI+poly clearance for a contracting job.  I'm in my early twenties and I'm addicted to social media like crack.

Does the background investigation for security clearances officially check your social networking and online presence now?  If so, how do background investigators (BI's) do this?   
Will they ask for your social media account usernames or URLs?   
Will they ask for your login passwords?

If BI's do not officially do this, do they do it unofficially, such as just Googling a candidate and poking around the popular social networking sites for hits?

What if your social media pages are private so that only your accepted friends can view them?  Will government agencies ask you to make your accounts public so that they can view the pages?

What unacceptable things on your social media can disqualify you from a clearance?

What about polygraph questions, have they changed at all in the past couple of decades to include anything about an applicants online presence?

I did not see anything on the SF86 about social media accounts.  I find it hard to believe if checking an applicant's digital footprint is not part of the process now, whether officially or unofficially.


I found this interesting thread on Quora but cannot verify the authenticity of it.
Anyone can chime in and enlighten me.