Had my fishbot running for a bit today, went to go watch some TV. Came back to grab my coffee and saw that I died. No big deal, right? Just soul walk and restart what I was doing. Checked my combat log to see if someone PvP'd me or something. Nope.
Fisherbot 9000 is an automated service put in by Trion to prevent fishbotting, since it's a pretty big issue in this game. What it does is goes around to kill people 20+ levels below the area that they are fishing in. My char is level 16, fishing in Shimmersand.
Seems like a pretty basic prevention method though, just level your alt a bit and you won't get bothered anymore.
source (near the bottom, crafting section)
video