WASHINGTON—Authorities are investigating whether Mitt Romney's private email account was hacked, his presidential campaign said Tuesday.

The website Gawker reported Tuesday that an anonymous hacker had signed into Romney's personal Hotmail account. Gawker reported that the hacker guessed the answer to a security question about Romney's favorite pet in order to gain access to the account and change the password. The anonymous hacker told the website that Romney's account on DropBox, a file sharing service, also was compromised.

Romney's campaign said that "proper authorities are investigating this crime." Campaign spokeswoman Gail Gitcho refused to comment further and would not say who was investigating. She also would not say whether Romney still uses the Hotmail account.

Romney isn't the first politician to face security problems with a private email account. Just weeks before the 2008 presidential election, a Tennessee college student accessed the private emails of Republican vice presidential nominee Sarah Palin. The student, David Kernell, was convicted in April 2010 after Palin and her daughter Bristol testified about harassment and disruption they suffered. Kernell had correctly guessed answers to security questions guarding Palin's account, giving him access.

Romney's private Hotmail account was accepting email as recently as March 2012. As of Tuesday evening, the address was returning emails as undeliverable, citing an "unknown address."

Romney's private email address, mittromney(at)hotmail.com, was included in documents obtained and published earlier this year by The Associated Press. It was also included in documents attached to a Tuesday Wall Street Journal story. The address became public because Romney used it to conduct state business when he served as governor of Massachusetts, and some of his private emails were obtained under the Massachusetts Public Records Law.

Romney has used both a Hotmail account and an email account linked to his mittromney.com presidential campaign website. In August 2006, Romney told a group of recipients that all future emails were to be directed to the mittromney.com campaign account.

Romney wrote that, effective immediately, the new account would be his new email address. "Please keep it confidential as its use is for family and close friends," he wrote. "I will no longer be using my Hotmail account."

One month later, Romney again used the Hotmail address to email revisions of an editorial he was writing.

In March, the AP sent emails to each of Romney's private accounts. Both appeared to be operative at that time, but he did not reply. A Microsoft spokeswoman said Hotmail accounts are closed after 270 days of inactivity and incoming emails sent afterward are rejected as undeliverable. Neither of Romney's accounts bounced messages back to the AP in March.

An email sent to his private Hotmail account Tuesday bounced back as undeliverable.

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