An '08 paper from Arvind Narayanan and Vitaly Shmatikov at the University of Texas at Austin showed that, in a large dataset, the combination of a large number

An '08 paper from Arvind Narayanan and Vitaly Shmatikov at the University of Texas at Austin showed that, in a large dataset, the combination of a large number of transactions could be used to de-anonymize individuals. http://www.cs.utexas.edu/~shmat/shmat_oak08netflix.pdf http://www.cs.utexas.edu/~shmat/shmat_oak08netflix.pdf