1x1x1x1 is an infamous hacker who helped carry out the April 1st hack, the biggest hack on Roblox ever. Before 1x1x1x1 carried out the April 1st hack he used to go into games and exploit them. If you don't know what an exploit is, it's a software tool designed to take advantage of a flaw in a computer system, typically for malicious purposes such as installing malware. His most famous exploit is the raining heads one.

1x1x1x1

Next one is C00lKidd - yes thats how its spelt with two zeros. Anyway c00lkidd was anthor exploiter not really a hacker but he is still very famous he was the owner of the group team C00lKidd. He also developed a software called C00lKidd GUI, it was frequently used by him and other exploiters. The GUI could allow you to fly, change your walkspeed and insert assets into infected servers. He has exploited work at a pizza place and the more popular natural disaster survival games.

c00lKidd