A Bloom filter is a data structure that allows computers to see if a given element occurs in a set. Bloom filters use hash functions to do this. For each element that is added, a hash value is calculated. When a new element is added, its hash value is compared to that of the other elements in the set. A Bloom filter is a probabilistic data structure. It is possible to get a false positive, but not to get a false negative. In other words, a query returns either "possibly in set" or "definitely not in set". Elements can be added to the set, but not removed. For each added element, the probability of getting a false positive grows. 