I've used AVG Free on all my systems for a few years now and haven't had any problems.

I've also controlled electronics I've built using ethernet, USB and serial ports either directly connected to the boards themselves or through microcontrollers (Atmel and Microchip) without any problems. Most boards I make are full duplex, both sending and receiving information, so if there was a problem I would likely have noticed it already.

You should be OK I think.

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