"...The Associated Press later identified Stanley, Inc. as the Virginia-based contractor whose two employees were terminated."... Stanley's CEO was a political donor to the campaign of Sen. Joe Lieberman, "a leading supporter of Obama's Republican adversary John McCain. In March 2005 Nolan gave $1,000 to Lieberman's reelection campaign."...
The NBC News 'Deep Background' blog has more on Stanley as well as another firm involved in the breaches, The Analysis Corporation of McLean, including the revelation from public records that Stanley CEO Nolan "gave $1,000 to Sen. Hillary Clinton's presidential campaign on Feb. 20, 2008" and Analysis CEO John Brennan "gave $2,300 to Sen. Obama on Jan. 28, 2008."...
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That article also provides more information about the information in passport files and how it can be used-
"It is not clear whether the employees saw anything other than the basic personal data such as name, citizenship, age, Social Security number and place of birth, which is required when a person fills out a passport application.
Aside from the file, the information could allow Obama's critics to dig deeper into his private life. While the file includes his date and place of birth, address at time of application and the countries he's traveled to, the most important detail would be his Social Security number, which can be used to pull credit reports and other personal information"...
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Furthermore, that article includes the information that
"The disclosure of inappropriate passport inquiries recalled an incident in 1992, when a Republican political appointee at the State Department was demoted over a search of presidential candidate Bill Clinton's passport records. At the time he was challenging President George H.W. Bush.
The State Department's inspector general said the official had helped arrange the search in an attempt to find politically damaging information about Clinton, who had been rumored to have considered renouncing his citizenship to avoid the Vietnam War draft".