The Chicago Tribune says it has compiled a list of 2,653 CIA employees, just by searching the Internet.
The newspaper said it gathered the information from online services that compile public data, that any fee-paying subscriber can access.
It did not publish the names, at the CIA's request. Many of the agents are believed to be covert. The paper also located two dozen "secret" facilities.
A CIA spokeswoman admitted the Internet had scuppered some of its methods.
"Cover is a complex issue that is more complex in the Internet age," said Jennifer Dyck.
"There are things that worked previously that no longer work. [CIA Director Porter] Goss is committed to modernising the way the agency does cover in order to protect our officers who are doing dangerous work."
Ms Dyck declined to detail the remedies "since we don't want the bad guys to know what we're fixing".
The Chicago Tribune article was headlined: "Internet blows CIA cover."
It began: "She is 52 years old, married, grew up in the Kansas City suburbs and now lives in Virginia, in a new three-bedroom house."
It went on to explain that the online service describes the woman in question as a CIA employee who has been assigned to several American embassies in Europe.
The CIA confirmed that she was a covert operative.
The paper also identified facilities in Chicago, northern Virginia, Florida, Ohio, Pennsylvania, Utah and Washington state. It said some were heavily guarded, but others appeared outwardly to be private residences.
Asked how so many personal details of CIA employees had found their way into the public domain, a senior US intelligence official told the Tribune "I don't have a great explanation, quite frankly".
Asked about fears that the details might be accessed by terrorist groups, he replied: "I don't know whether al-Qaeda could do this, but the Chinese could."
The disclosure comes as the US justice department continues an investigation into whether members of the Bush administration deliberately exposed the identity of CIA operative Valerie Plame.
UKFast is not responsible for the content of external Internet sites.