RepeatMasker is a program that screens DNA sequences for interspersed repeats and low complexity DNA sequences. The output of the program is a detailed annotation of the repeats that are present in the query sequence as well as a modified version of the query sequence in which all the annotated repeats have been masked (default: replaced by Ns). On average, almost 50% of a human genomic DNA sequence currently will be masked by the program with the use of the default settings. Sequence comparisons in RepeatMasker are performed by one of several popular search engines including, cross_match, ABBlast/WUBlast, RMBlast and Decypher.