(A) In IBS tiling a user (called the 'adversary') uploads multiple public genomes (shown in yellow) to a DNA matching service in order to determine the sequence of a target genome (pale blue) that is already present in the service's database. In the figure, uploading the first genome yields three IBS segments (a,b,c; pale green), uploading the second genome yields two (d,e), and uploading the third genome also yields two (f,g). IBS tiling only works if the matching service reports matching IBS segments and their locations between the public genomes and the target genome (see text). The amount of information obtained by the adversary increases with the number of public genomes uploaded to the service. (B) In IBS probing, the adversary uploads a 'probe' genome that belongs to a person who is known to carry an important mutation (such as a mutation that causes a disease; red star). If the target genome contains the same mutation, the DNA matching service will (under certain conditions) report a matching IBS segment, and the adversary will know that the target also has this mutation in their genome. In general, IBS probing is expected to work for mutations that are relatively young (that is, less than about 500–1000 years old).