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Rogelio V. Solis, Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney speaks at the Mississippi Farmers Market in Jackson, Miss., Friday, March 9, 2012.

WASHINGTON — Documents obtained by The Associated Press show that Republican presidential candidate Mitt Romney and some of his top aides used private email accounts to conduct state business at times when Romney was governor of Massachusetts.

The communications were legal, even though Romney's own administration warned state agencies against the practice due to cyber security concerns. The state archives in Massachusetts, which learned about Romney's emails from the AP, says the private emails should have invoked rules about preserving copies of state records. Romney's campaign said he complied with all state laws.

The private emails raise questions about why Romney and his aides sometimes bypassed the official email system. Such private email accounts are effectively off limits to public review because they're often used secretly.