Bacteria have many ways to resist being exploited by bacteriophage viruses, including the adaptable CRISPR/Cas system that uses a piece of viral nucleic acid sequence to target and destroy incoming phages. But phages also have many ways to evade and disrupt bacterial defenses.

In this study, a phage is discovered that inserts its own genome into the CRISPR/Cas sequence in the bacterial genome, disrupting the bacterial defenses. To escape the defenses while it is doing this insertion, it carries genes for previously-unknown anti-CRISPR proteins. But inserting and removing a viral sequence from the bacterial genome is not always a clean procedure.