...the presidential transition team discovered that the nominee had not paid Social Security taxes when he worked for the International Monetary Fund from 2001 to 2003, nor in 2004, when he also received compensation from the fund.Quick breakdown on Geithner. He was employed overseas, basically as an independent contractor. He is paid the full amount, nothing withheld. The onus is on him to pay all his taxes, income, social security, etc. When he does pay he signs a form saying that he has paid and is reimbursed for the paid (or in his case, unpaid) taxes. And it went on for four years.
The IMF does not withhold those taxes from its employees' pay, so employees are supposed to pay so-called self-employment taxes themselves.
This will be the man in charge of enforcing the tax code for the next four years if confirmed.
Michelle has more on the details of the 'simple mistake'.