Backpowering via analog inputs?

Hello all,

I recently was doing an experiment where i had a power supply hooked up to a relay. When the relay was triggered (closed), 5v from the power supply was supposed to be read by A0 on the arduino, and then pull up a digital I/O. However, it seems that the Arduino is somehow being powered by the analog input? How is this possible? Is this bad? Did i damage my board? Help!

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Gotcha. Thanks for the reply, i only had it backpowered for maybe 5 seconds, and the board seems to be ok so im guessing this time i got off lucky. I changed around my circuit design and fixed the problem so this wont continue to happen