What is the largest security company?

I'm curious, could you please clarify which security company you are referring to as the largest? Is it in terms of market capitalization, revenue, number of employees, or perhaps a different metric? It would be helpful to have a clearer understanding of the context in order to accurately answer your question. Additionally, the security industry is vast and encompasses various sectors such as cybersecurity, physical security, and financial security, so specifying the particular sector of interest would also be beneficial.