Tax data for up to 330,000 households might have been stolen.

The Internal Revenue Service said Monday that more than twice as many taxpayer accounts were hit by identity thieves than the agency first reported, with hackers gaining access to as many as 330,000 accounts and attempting to break into an additional 280,000. The IRS said in May that cyber crooks used stolen Social Security numbers and other data acquired elsewhere to try to gain access to prior-year tax return information for about 225,000 U.S. households. That included about 114,000 successful attempts and 111,000 unsuccessful ones. The agency said Monday that further investigation showed an additional 390,000 taxpayers were potentially affected, including about 220,000 accounts where hackers cleared an authentication process and about 170,000 failed attempts. The earlier investigation covered the period of February to May. This time the agency conducted a deeper review that looked at data from as far back as November 2014. The new revelations are likely to add to the beleaguered agency’s public-relations problems, at a time when many lawmakers—particularly Republicans—already are unhappy over its performance on several fronts.

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