I think that you have opened E-Mail with a Virus in it. Or a spam E-mail. I receive 2-4 such E-Mails every day and I delete them. I looked at bleepingcomputer forum, but now they have no any solutions to zepto-ransomware-virus because it is rather new one. I found some informations on a german virus-decryption-page:
http://www.virus-entferner.de/2016/0...rus-entfernen/
May be it can help you. They write that Recovery Pro Program and PC Healp Advisor Paretologic Program can solve the decryption of this ransomware.