Since a few days now, people trying to plan a trip on Deutsche Bahn's (DB) main booking website have been getting stopped by error 751. The site accused their web browser of acting like a bot, and even logging into accounts made no difference.So, what was actually triggering it? Just the word "Linux" in the User-Agent string it looks like. heise online tested this by setting a Linux User-Agent on Firefox under Windows and on Safari under macOS, and both got blocked.People noticedSource: MaksDampfHeise had picked up on a thread from Reddit's r/deutschebahn as evidence that real users were being affected. Someone had posted about getting locked out just from clicking "earlier connections" a few times while planning a trip.They, as you know, tested it on their end and found out that Linux systems were being blocked.Later in the thread, a commenter tied it to the wave of vibe-coded projects, specifically ones built to scrape Deutsche Bahn's fare data. Another commenter identified themselves as a DB employee, pointing out that internal staff have to deal with DB Systel's problems regularly. Before you ask, DB Systel is the train operator's IT and digital solutions provider.DB's official responseDeutsche Bahn has responded to heise online. A spokesperson said Linux users are supposed to be able to use bahn.de and DB Navigator without issues, and that the company's security systems look at traffic behavior, request origins, and browser traits to identify potential threats.Normal traffic can get caught in this sometimes, they said, while emphasizing that they are working to bring those cases down. Heise ran a test again the same day and found out that a Linux User-Agent on a Windows machine still triggered the block.I ran two tests of my own. The first was on a Fedora Workstation system with a VPN active, where I accessed bahn.de on Firefox in private mode and spammed various header menu options, reloading repeatedly.The portal never locked me out. I did the same on an Ubuntu virtual machine and got the same result. So it is safe to assume the fixes have been made, though false positives may still happen occasionally.Suggested Read 📖: Rust Could Eliminate 80% of Linux Kernel CVEs