[ASM] - what is "Browser Challenge file" ?

The Browser Challenge File contains signatures and updates relating to ASM components such as Bot Defense, L7 DOS and other client-side browser checks and keeping it up to date maintains best compatibility and detections for both legitimate and malicious browser technologies.

To check and/or to update it, go to System->Software Management->Live Update:

See this article for further instructions: https://my.f5.com/manage/s/article/K40253074