A friend of mine was having a lot of really really weird network issues at one of their location in another city (B2B supply company). Ports randomly going up a

A friend of mine was having a lot of really really weird network issues at one of their location in another city (B2B supply company). Ports randomly going up and down on various equipment over the network. Appeared to be an electric issue, so we did various testing, ground bonding, etc. Added redundant equipment after that failed to be reliable. Having little else to offer in the way of suggestions, I made a joke that someone was using an etherkiller. Damned if I didn't end up being right. They had a clerk who was embezzling by creating false customer returns. Every time she made one she plugged the network into the mains. Her boyfriend apparently made this thing and told her that it would 'fuzz the system' or some other kind of idiotic idea. What it actually did was eventually start a small fire in the wiring closet. So, yeah the effect of one of these things is gonna be highly dependent on the environment. The galvanic isolation of Ethernet is not any sort of guarantee. Though I can confirm that the Cisco gear stood up to unreasonable abuse, it was unequivocally damaged.