Hacked on Jan 4, 2015, they closed for a week, reopened and seemed to have regained most of their customer base since that time by reacting with a complete overhaul on every level from the trading platform itself to the way security is handled.
https://www.coindesk.com/unconfirmed-report-5-million-bitstamp-bitcoin-exchange/
Thanks for your explanation and that link..!! :)