Information storage in DNA is the cornerstone of biology. Interestingly, prokaryotes can store information in specific loci in their DNA to remember encounters with invaders (such as bacteriophages--viruses that infect bacteria). Short samples of DNA from invaders are inserted as "spacers" into the CRISPR array. The array thus contains samples of DNA invaders in a defined locus that is recognized by Cas proteins that further process this information. This enables bacteria to adaptively and specifically respond to invading DNA that they have experienced before.