Viruses are, as we have seen over the past year, very proficient at invading a host and subsequently reproducing rapidly. Our adaptive immune system, after a first encounter with a virus, can store information about the outside protein shell and use this information to destroy the virus in later encounters. Bacteria have an adaptive immune system that works on the nucleic acid level (DNA/RNA). The right functioning of the system demands that a fragment of a virus is incorporated into the bacterial genome correctly (adaptation). Subsequently, proteins carrying copies of this fragment have to find and destroy the virus quickly enough after it enters the cell (interference). An obstacle in the interference process is that the cell is filled with host DNA, which has to be scanned to differentiate it from viral DNA. How bacteria are still able to find these viruses fast enough is the subject of my thesis.