What are the different types of messages in FIX?

Could you elaborate on the various types of messages that are used within the Financial Information Exchange (FIX) protocol? I understand that FIX is a widely adopted messaging standard in the financial industry, particularly for the electronic trading of securities. Are there specific message types designed for different types of transactions, such as orders, executions, or market data? And do these message types adhere to a standardized format, ensuring interoperability between various systems and participants in the market? Additionally, are there any security measures in place to ensure the integrity and confidentiality of these messages? I'm curious to learn more about how the FIX protocol facilitates efficient and secure communication in the financial industry.