Um, ok... I ran the H&H client and... uh... my computer... crashed. Yes. And it blue screened. Really bad, too.
The hard drive got completely corrupted.
And then the power supply overheated, causing a fire and sending a spike back up to the transformer, which exploded and shorted out the local grid, causing an EMP pulse and telecommunications blackout that caused the local missile silo to suspect a nuclear attack... and by this time I got my computer back up an running again... erm, apparently on a generator and with WAN internet. Then I ran H&H again and logged in, but apparently instead of sending my login to the server, it accidentally sent the launch codes to the silo, causing them to launch a retaliatory attack on Russia and North Korea.
So basically, the bug is that running H&H causes thermonuclear holocaust, though it's intermittent.