How to secure loose power wires?

I've recently acquired a PC with a PSU in which somebody has pulled 4 wires out of a molex connector, so now these wires are loose with exposed metal. There are two black and two yellow, and whoever did this had the exposed wiring at the end of the black cables twisted together and the exposed wiring at the end of the yellow cables twisted together. It doesn't seem safe or wise to to me to use the the PSU as it is. Should I leave these wires twisted together as they are? Should I cover the exposed wiring in electrical tape or something else? Less importantly, why would somebody do this?

Yea just wrap them up good in electrical tape and all should be good.