GFW actively probes obfs2 bridges
It looks like the GFW is now actively probing obfs2. After hearing rumours yesterday, I wasn't able to reproduce this. Today, however, I got my private obfs2 bridge probed just milliseconds after my own connection from China. I got hit by two random Chinese addresses as we already know it from the Tor probing. After the probing, my obfs2 connection timed out and the SYN/ACK segments from the bridge were dropped when trying to establish a new connection. I could reproduce all of this several times.
I haven't tested obfs3 yet and I suppose we can skip the old looking-for-the-fingerprint game. Depending on what protocols they are trying to detect, they might have to probe several times since it's not clear what's behind all that entropy. It might be obfs2, obfs3 or VPN PSK and perhaps even more protocols.