WASHINGTON (CNN) --
The security of the passport files of the top presidential candidates was breached, the State Department says.
John Brennan, president of the Analysis Corp., advises the Illinois Democrat on foreign policy and intelligence issues, the source said.
Brennan briefed the media on behalf of the campaign this month.
The executive is a former senior CIA official and former interim director of the National Counterterrorism Center.
He contributed $2,300 to the Obama campaign in January. Watch how Brennan and another contractor exec are linked to campaigns »
When asked about the contribution, a State Department official told CNN's Zain Verjee, "We ethically awarded contracts. Political affiliation is not one of the factors that we check."
On Friday, the department revealed that Obama's passport file was improperly accessed three times this year, and the passport files of the two other major presidential candidates -- Democrat Hillary Clinton and Republican John McCain -- had also been breached. Watch the secretary of state apologize for the breach »
Three contractors are accused in the wrongdoing, including the one who works for the Analysis Corp. and who was disciplined. That contractor accessed McCain's file in addition to Obama's. None of the contractors was identified.
The Washington Times, which broke the story Thursday night that Obama's records had been improperly accessed, reported Saturday that the State Department inquiry is focusing on the Analysis Corp. employee. Also, the investigation by the department's inspector general will include polygraph tests for supervisors in the passport section to find out whether there was any political motive.
The other two contractors who worked for Stanley Inc. were fired.
"While this is a rare occurrence, we regret the unauthorized access of any individual's private information," the company said in a statement Friday.
Stanley has had contracts with the department since 1992 and was recently awarded a $570 million contract to continue providing support for passport processing. Its CEO, Philip Nolan, contributed $1,000 to the Clinton campaign.
The department official said the three contractors worked in three offices in the Washington area that are involved in various functions. One office does consular work and visas on evenings, holidays, weekends and overnights; another office issues passports; the third office scans and files materials.
The source said there has been no problem in the past with the Analysis Corp. employee, who has "extensive" experience. The worker has been with the company for years and has always worked under a State Department contract.
Explaining that the department had "complimented" this person for work in the past, the source said the individual is considered a "terrific" employee, except for this one instance, characterized as an "aberration."
The department asked the Analysis Corp. not to take any administrative action against the employee while the investigation is under way.
On Friday, the company released a statement saying it would fully cooperate with the federal investigation. The source said the Analysis Corp. has told the employee to do the same.
Echoing the State Department spokesman Friday, this source said there is no indication the motivation was anything but idle curiosity.
The source said the Analysis Corp. first learned of its employee's actions Friday morning when it received a call from the State Department. In its statement, the firm confirmed that one of the contractors was an employee and called it "an isolated incident." E-mail to a friend