There’s an old IT saw… there are two kinds of companies: those who know that they have been hacked and those who don’t.

The FBI warned the Clinton campaign that it was a target of a cyberattack last March, just weeks before the Democratic National Committee discovered it had been penetrated by hackers it now believes were working for Russian intelligence, two sources who have been briefed on the matter told Yahoo News.

In a meeting with senior officials at the campaign’s Brooklyn headquarters, FBI agents laid out concerns that cyberhackers had used so-called spear-phishing emails as part of an attempt to penetrate the campaign’s computers, the sources said. One of the sources said agents conducting a national security investigation asked the Clinton campaign to turn over internal computer logs as well as the personal email addresses of senior campaign officials. But the campaign, through its lawyers, declined to provide the data, deciding that the FBI’s request for sensitive personal and campaign information data was too broad and intrusive, the source said.

A second source who had been briefed on the matter and who confirmed the Brooklyn meeting said agents provided no specific information to the campaign about the identity of the cyberhackers or whether they were associated with a foreign government. The source said the campaign was already aware of attempts to penetrate its computers and had taken steps to thwart them, emphasizing that there is still no evidence that the campaign’s computers had actually been successfully penetrated.

But the potential that the intruders were associated with a foreign government should have come as no surprise to the Clinton campaign, said several sources knowledgeable about the investigation. Chinese intelligence hackers were widely reported to have penetrated both the campaigns of Barack Obama and John McCain in 2008.