The facts don't match the spin and conspiracy theories put forth by Sanders supporters. I don't believe Sanders personally was involved or was aware, however it's clear some of his staffers went data fishing looking for very specific info:
***Another person familiar with the investigation also told NBC News that a total of four individuals affiliated with the Sanders campaign appear to have accessed the data, including Uretsky and Deputy National Data Director Russell Drapkin.
A series of documents outlining an audit trail maintained by the database company, obtained and reviewed by NBC News, shows that the four individuals spent a total of about 40 minutes conducting searches of the Clinton data. Those searches included terms that point to Sanders’ team gaining access to proprietary lists from more than 10 early voting states of Clinton’s likely supporters as well as lists for Sanders backers. That data was saved to personal folders.
It also appears that Drapkin “suppressed” two folders after the database company became aware of the breach.
The Clinton campaign learned of the breach on Wednesday, a source told NBC News.***
http://www.msnbc.com/msnbc/documents-show-sanders-staffers-breached-clinton-voter-data
