It seems that the internet provider you're using when you get those messages - Hydra in France - has got itself onto a list of naughty networks at Cloudflare, and Internet Brands - the people who run and host Flyertalk have applied various defensive controls at Cloudflare to protect the website and forum. Unfortunately flyertalk gets more than it's fair share of bad people trying to do inappropriate things to flyertalk and Internet Brands appear to be quite aggressive with the controls available to protect the service.