The Anti-Green Lantern Corps are artificial beings who were created when the Weaponers of Qward completed a century-long task of forming a mockery of the Green Lantern Corps, empowered by their own rings. However, these anti-rings were very volatile and thus the Anti-Green Lantern Corps had very short life spans as a result.
Made en mass the Anti-Green Lantern Corp grew to at least 2000 members before they clashed with the Green Lantern Corps proper - the Weaponers of Qward had hoped to capture Hal Jordan and use his ring to further empower the group but he successfully overpowered them.
After a battle involving 200 Green Lanterns and 2000 Anti-Green Lantern Corps Arisia, Hal Jordan and Katma Tui teamed up to successfully shatter the Central Power Battery of the Anti-Green Lantern Corps, which caused their rings to become useless and forced the group to disperse.
They have not been seen since this incident or even mentioned again in-universe (though the story is often reprinted, as recently as 2006).