Research has uncovered a novel role of the CRISPR-Cas9 system, revealing that Cas9 acts as a guardian in bacterial immunity. Initially discovered in the early 2000s as a mechanism bacteria use to defend against viral phages, CRISPR-Cas9 technology revolutionized genome editing. The current findings show that beyond its genetic editing capabilities, Cas9 plays essential roles in defending bacteria from viral infection, expanding biological understanding of this molecular tool.