Forty-four percent of Fortune 500 companies have had their employees' stolen email addresses and passwords exposed in Internet forums used by hackers this year, giving criminals potential entrée to customer data and critical U.S. infrastructure, according to a new report.

The data firm Recorded Future scoured Internet forums and "paste sites" – web applications typically used to share computer code -- from Jan. 1 through Oct. 8 to uncover the vulnerability involving employee "credentials" – the combination of an email address and password. Recorded Future found that 221 of the nation's top companies had employee credentials exposed, including 51 percent of the leading financial firms, 62 percent of technology firms and 49 percent of public utilities.