The company said it had no indication that any of its user accounts were improperly entered, and that it had notified the users and made them reset their passwords on the accounts.
The company learned of the theft of the data only two weeks ago after the 68 million user credentials were posted online, but indicated it still does not know how or by whom.
"The list of email addresses with hashed and salted passwords is real, however we have no indication that Dropbox user accounts have been improperly accessed. We're very sorry this happened and would like to clear up what's going on," the company said in an emailed statement.
"This reset ensures that even if these passwords are cracked, they can't be used to access Dropbox accounts."
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Dropbox warned users that if they had signed up for its services before 2012 and had used the same password elsewhere, they should change that as well to protect the account.
"Also, please be alert to spam or phishing because email addresses were included in the list," it said.