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Chief Intelligence Correspondent Catherine Herridge discussed how the FBI came upon the new cache of Clinton-related emails while investigating disgraced former Rep. Anthony Weiner (D-N.Y.), On The Record with Brit Hume.

While scouring the metadata of emails stored on Weiner's wife, Huma Abedin's, computer, they found tens of thousands of messages that were allegedly sent to or from Hillary Clinton's private email server.

The metadata, Herridge said, can be compared to the address bar on a postal letter--where the recipients and senders can be seen, but not the correspondence therein.

Agents were probing the computer's contents in connection to their probe into allegations that Weiner sent sexually explicit messages to a minor in North Carolina.

FBI agents obtained a warrant to dig deeper, and developed a program so they can scour the tens of thousands of emails at a quicker pace.

Herridge said agents must then take the pool of data they collect and narrow it down--"what's new, what's partial--part was handed over [to investigators in the Clinton probe], part was not".

A source close to Anthony Weiner's legal team told Fox News' Bret Baier that in an effort to back up her cell phone contacts onto her computer, the machine backed up Abedin's emails as well.

Processing all of the new information effectively and appropriately in a short time window "will be very tough," Herridge said.

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