Go to Google Security Checklist and review your information. It will take only a minute and Google will give you 2 GB of free Google Drive storage. The 2 GB extra space is permanent!
You need to complete the checkup by 17 February 2015 and you'll get the free storage at the end of the month.
After you've gone through the checkup successfully, you'll see three green checkboxes (see below) that confirm you're eligible for the free storae.
Source: Google Drive Blog