AOL CEO Tim Armstrong REUTERS/Jim Urquhart A number of AOL user accounts may have been breached, which means that sensitive personal information such as email addresses, passwords, postal addresses and answers to security questions might have been compromised, AOL wrote in a blog post first spotted by Market Watch.

AOL said on Monday that it's currently investigating a security situation that involves unauthorized access to a significant number of user accounts.

There's no indication that financial information has been obtained from these breached user accounts. The encryption codes being used to protect passwords and security questions also seem to be in tact, the blog post says.

AOL said the following in its post:

We are working closely with federal authorities to pursue this investigation to its resolution.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 company said it began investigating the matter after it noticed a big increase in the number of spam emails appearing as "spoofed" emails from AOL accounts. "Spoofed" emails are messages sent from imposter email addresses that are meant to imitate a legitimate user account. In most cases, these email addresses are lightly edited to change a few characters iso that recipients are tricked into opening the email.

AOL said it believes that spammers have used contact information to send spoof emails imitating roughly 2% of its email accounts.

Last week, reports indicated that a number of old AOL email accounts had been hacked to send out spam emails. One victim even reported that phishing emails had been sent to 2,200 contacts, according to GigaOM.

AOL is currently encouraging users to change their passwords and security questions.