Chains is the name of two hackers, Cháins and Chaíns. They are believed to be the hackers behind Phobia another group of hackers. More seems to be known about the group they own then themselves, pretty much all we know is they are the people behind the hacking group.
As already stated, not much is known about them. They haven't done anything to really make themselves noticed yet.
What do they do
Chains don't seem to do anything but they seem to use Phobia to hack. Phobia usually surround the person they want to hack.