AOL is investigating a security breach where unknown attackers infiltrated a "significant" number of accounts to access email addresses, passwords, security questions and more.

According to AOL, the incident did not appear to involve broken encryption, and there is no indication that users' financial information was hacked, The Wall Street Journal's MarketWatch reported.

The company began looking into the matter when the amount of a certain kind of spam email recently spiked. Known as "spoofed emails," this particular form of spam uses edited addresses so the emails look as if they come from legitimate accounts, making them more likely to be opened.

"These emails do not originate from the sender's email or email service provider--the addresses are just edited to make them appear that way," AOL said in a statement quoted by FOX Business.

AOL is reaching out to affected accounts, but all users are encouraged to set up new passwords and security questions.  

"We are working closely with federal authorities to pursue this investigation to its resolution," AOL said, as quoted by MarketWatch. "Our security team has put enhanced protective measures in place and we urge our users to take proactive steps to help ensure the security of their accounts."

The New York-based company has not disclosed the number of accounts likely affected in the security breach, but it has said that the spoofed emails appear to have been sent from about 2 percent of all AOL accounts.

The breach follows other security incidents such as the Target fiasco last year when millions of customer accounts were compromised or the multiple privacy issues seen in social networks, including Facebook, Twitter and Snapchat. 

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