How do companies profile people based on social media?

[Andria]

I have been hearing a lot about how what you do on social media, like twitter facebook etc. is logged and compiled by companies and organizations.

So, when you go to apply for a job or for a college they will have a profile on you and what you've done and what you write based on your social media presence.

My question is, let's say I am a company and I want to hire someone. But it's a secret information sensitive, with confidential documents and such, so I want to know exactly who this person is.
How would I go about collecting this information.
Would I have one of my people scour the internet for this persons profile.
or are there companies that compile databases on each person.

I would just like to know how exactly this works.

Thanks in advance.

[Aj]

Most companies will limit themselves to what is readily and easy available via social networks like fb and even linksys. However, in some cases and for some positions they can have access to more professional paid databases like WorldCheck (see link) and they may even hire a forensic services company who will have even more means to do a background check into a potential employee.