I'm not sure where you're getting the 10.61.x.x addresses from. I'd guess it was your ISP -- which would explain why you could get new IPs and they would still work. The bad news about that is, if it is your ISP that means your internal network is 'leaking' out onto the Internet and everyone else who has 10.61.X.X IPs can see your internal network.
Who is your ISP?