1775 Sec followed up their original tweets by saying they were giving Dropbox time to resolve known vulnerabilities in the site before they dump the database.
They later laughed off the tweet about the database dump, claiming they had just performed a DDoS attack and nothing else.
We are literally choking on laughter! We DDoS attacked #DropBox. Claiming its a data breach! This is so ducking funny?-- The 1775 Sec (@1775Sec) January 11, 2014
UPDATE: Dropbox has denied wholeheartedly that "External Factors" led to the downtime.
Dropbox site is back up! Claims of leaked user info are a hoax. The outage was caused during internal maintenance. Thanks for your patience!— Dropbox (@Dropbox) January 11, 2014