Apparently we need to be aware of this. 

Clustered regularly interspaced short palindromic repeats (CRISPR, pronounced crisper[2]) are segments of prokaryotic DNA containing short repetitions of base sequences. Each repetition is followed by short segments of “spacer DNA” from previous exposures to a bacteriophage virus or plasmid.[3]

The CRISPR/Cas system is a prokaryotic immune systemthat confers resistance to foreign genetic elements such as those present within plasmids and phages,[4][5][6] and provides a form of acquired immunityCRISPR associated proteins (Cas) use the CRISPR spacers to recognize and cut these exogenous genetic elements in a manner analogous to RNA interference in eukaryotic organisms.[3]CRISPRs are found in approximately 40% of sequenced bacterial genomes and 90% of sequenced archaea.[7][note 1]