(Bloomberg) -- Hacking attacks designed to alter electronicdata, rather than steal it, may grow more common as terrorists andcriminals seek to undermine the integrity of financial markets inthe future, the head of U.S. intelligence is warning lawmakers.

“We might also see more cyber operations that will change ormanipulate electronic information in order to compromise itsintegrity,” Director of National Intelligence James Clappersaid in testimony prepared for a House intelligence committeehearing Thursday in Washington. “Decision making by seniorgovernment officials (civilian and military), corporate executives,investors or others will be impaired if they cannot trust theinformation they are receiving.”

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Clapper’s warning is one of the starkest to date about a new andpotentially debilitating form of hacking. U.S. authorities lastmonth broke up an alleged insider trading ring that relied onhackers to steal corporate press announcements, which were thenused to manipulate stocks by trading on the information before itbecame public.

Institutional checks and balances can help prevent themanipulation of data, Clapper said, citing the market monitoringand clearing functions in the U.S. financial sector.

The House committee is meeting as President Barack Obama’sadministration is debating whether to impose sanctions on Chinesegovernment officials and companies for hacking U.S. networks.

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“Chinese cyber-espionage continues to target a broad spectrum ofU.S. interests, ranging from national security information tosensitive economic data and U.S. intellectual property,” Clappersaid.

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Hacking attacks are increasing in frequency and sophistication,although the likelihood of a catastrophic attack is remote,according to Clapper.

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