I was spidering a website with Burpsuite and the automated Form Submission caused me to unknowingly deface the main page with "555-555-0199@example.com".
It took me a decent amount of time to notice but when I did I immediately worked to resolve the issue by finding an archive of the page and recreating the content by hand.
I doubt anyone but me noticed this, though I'm very concerned about the legality of what happened and should anything in the future happen would I be liable since it was just simple spidering of the website that caused this to happen...