What is the Worst Tech Mistake You Ever Made?

CraigEagle asks: "Mistakes are made every day. The more technical knowledge you have the bigger your mistakes can be. What is the biggest technology related mistake you have ever made?"

"In the interest of full disclosure, this is mine:

I was working at a Fortune 50 bank as a consultant. I was due to go on vacation for a week and the company did not have webmail. I decided that I would try forwarding emails to my corporate account. (I know this was a bad idea, and probably against several corporate policies.) I set it up so that any email that came in would forward to my consulting company's account. My mistake was I also left Delivery Receipt on. This was not Microsoft, it was Lotus Notes. The system began forwarding the incoming mail to my account. But then it would get a Delivery Receipt, which in turn would be forwarded to my account, which would generate another delivery receipt, ad infinitum. When I got back from vacation they claimed I had brought down the email system for 4 hours. This incident caused the bank to stop allowing consultants to set up email rules. What's your story?"