Researchers at security firm We Are Segment have discovered a vulnerability in Gmail, a distorted message shuts down the most famous webmail in the world. The flaw could be exploited to shut down Gmail by sending to the victim a specially crafted message, impeding the user from accessing his/her email address. The email is effectively received by the recipient, but he cannot open it and, after just a few moments, Gmail shuts down showing the Error 500 message.”]
Source: http://securityaffairs.co/wordpress/67623/hacking/gmail-shutdown-zalgo-text.html