Eventually, it became so deeply linked to personal data throughout the economy that it became a de-facto national identifier.
"For identity thieves, it's their magic key . . . that gets into every door," said Daniel J. Solove, a George Washington University law school professor who specializes in privacy law. Getting a number can make it possible for criminals to access to bank or credit-card accounts, establish credit to make purchases, or find someone they wish to harm.
Keeping Social Security Numbers Safe Although Social Security numbers are used by businesses throughout the economy, privacy advocates recommend that individuals take several steps to limit the distribution of their numbers.
Nonetheless, some insurance companies still use the Social Security number as an individual's account number, printing it on identification cards, leaving people vulnerable if wallets are stolen or lost. Medical offices routinely request Social Security numbers, often when initial appointments are made, and many universities use it as a student identification number.
According to a recent study commissioned by Unisys Corp., a technology consulting company, about half of large financial institutions use Social Security numbers to verify the identities of customers who call in for services. Some even use it to identify customers as part of the log-in process when they want to access accounts via the Internet.
So vital are Social Security numbers in this sea of information that ChoicePoint warned investors in a recent Securities and Exchange Commission filing that its business could suffer if the rules on distribution of Social Security numbers were tightened.
The mass breaches of data at ChoicePoint and LexisNexis forced the companies to be proactive.
Executives of both firms told Congress last month that for many of their non-law-enforcement clients, Social Security numbers would be truncated so that only five digits would appear on reports.
But plenty of sources of the information still exist. Using an intermediary, The Washington Post was able to obtain the full Social Security number of a reporter within 24 hours from two of three online providers the intermediary contacted.
Not all of the providers advertise Social Security numbers, and those that do promise to verify that the buyer has a legitimate reason for seeking the number, such as to complete tax forms of an employee or to find someone involved in a court action.
The intermediary, a security consultant who helped the Federal Trade Commission identify illegal data sales in 1999, told the providers he needed the number for tax purposes. Two providers accepted that reason without question or requests for documentation. A third provider refused to provide Social Security numbers.