I was doing a Border Patrol mission in Deneb E7 when I had the unfortunate luck of meeting an invisible bot! Once I got there, I came under attack from three bots- a Serco Centurion, and Assault II, and a patch of empty space firing tachyons. Needless to say, the invisible bot killed me. Here's a purty picture for you that like 'em. Note the stream of tachyons coming from the left.

http://www.roguelazer.com/vimages/Roguelazer/invisible_bot.jpg

Yep. Had one yesterday...Not visible, didn't show on radar. It's shots were very effective though.

Same here, in Nyrius F8, in a storm sector. It appeared as if only one Guardian was chasing me, so I turned to explain him why is it such a bad idea. As I got into dogfight, I noticed shots coming from empty space as well. Luckily I was able to finish the visible one with about 92% of hull integrity. I ran before the other, invisible one, because it was untargetable and its shots stung...

Ancient Chinese curse..."May you live in interesting times!"