Possible Hacking of Server/Broken?

Hi, sorry I wasn't exactly sure where to post this. I've had my own bukkit server running for around 2 weeks now, and tonight I started it to find an odd IP address connecting on the wrong port (61000 something) and 'taking too long to log in' so I connected to the server to find a '437614' player connected. I wasn't sure what to do as I have never ever seen a username which is just numbers, and the IP was odd/wrong port so I immediately kicked it, to which it instantly reconnected before I could ban it fast enough. Can anyone tell me what just happened?