My wallet is fully up to date with the new block chain.

I tried setting listen=1

That results in peers with "version" : 60007, connecting to me.

1) Is there a danger they could screw up my block chain? 
2) Them being connected, does it slow performance with the valid peers?
3) Is there a way to "listen" but reject peer with "version" : 60007,?

Thanks,
Jason