Which of the following is NOT a factor that increases food vulnerability to biological attack?

The correct choice is based on understanding the factors influencing food vulnerability to biological attacks. A long shelf life is generally known to be a protective factor for food rather than a vulnerability factor. Foods that can be stored for extended periods are typically treated and processed to eliminate or reduce the potential for biological contamination, making them less susceptible to biological threats.

In contrast, foods with high moisture content create a favorable environment for microbial growth, making them more vulnerable to biological agents. Similarly, high protein content is often associated with a rich nutrient source for pathogens, thus increasing vulnerability. Easy distribution, while advantageous for getting food to areas in need, can also lead to quicker contamination spread if not managed properly. Therefore, a long shelf life serves as a mitigative factor against food vulnerability to biological attacks, making it the correct choice in this context.