717 GB. That's how much one person lost after asking Claude to help with a file operation. A single backslash in a generated command caused the AI to wipe an entire Windows installation clean.
This isn't a story about Claude being malicious or buggy in the traditional sense. It's a story about what happens when you give an AI agent unrestricted access to your file system and trust it to handle path parsing correctly - and it doesn't.
The Backslash That Ate Everything
Windows uses backslashes as directory separators (C:\Users\Documents). Unix-style shells - including the terminals that most AI coding tools operate in - use forward slashes. When Claude generated a deletion command, something went wrong with path interpretation. The backslash that was supposed to point at a specific folder caused the command to target a much larger scope instead. 717 GB, gone.
The failure mode matters because it's a known hazard in cross-platform environments. A path like C:\Users\George\old-project passed to a Unix shell command can be parsed in unexpected ways. If the backslash gets misread, the target path changes entirely. Developers have hit this for decades. But when a human writes the command, they usually read it before pressing Enter. When an AI agent executes it autonomously, that review step disappears.
What AI Agents Actually Do With File Access
Claude Code and similar tools - Cursor, Aider, Cody - can read and write files, run terminal commands, and chain operations together. That's what makes them genuinely useful: you can say "clean up my old build artifacts" and watch it happen without writing a single line yourself.
But useful and safe aren't the same thing.
Most AI coding tools include safety prompts that flag risky operations before running them. Claude Code specifically surfaces warnings on destructive commands. But those prompts get clicked through, especially when you're deep in a debugging session and just want the problem solved. The AI does what you approved. It doesn't second-guess the path.
Think of an AI agent like a very fast contractor who does exactly what you say, without necessarily understanding the full context of what's being touched. A contractor new to your house would probably ask twice before opening walls. Your AI agent might not ask at all.
What To Actually Do Before the Next Session
Back up before giving any AI agent file system access - not as abstract advice, but as a before-you-start step. A snapshot to an external drive or cloud backup takes under 10 minutes on most machines and covers you against exactly this kind of cascading failure.
For anything involving bulk deletion, path manipulation, or operations that cross Windows and Unix environments: read the generated command before it executes. Every serious AI coding tool has a preview or explain mode. For destructive operations, use it every time.
The person who lost 717 GB probably won't make that mistake twice. You don't have to make it once.