Mind Hacking is a skill that is born in certain individuals. Delta states that he was born a Mind Hacker because his parents had esper abilities (both his mother and father are SHIFTers) and their reproductive cells underwent epigenetic changes due to the stress of the Decision Game. It is unknown if people with this skill can be born to non-esper parents.
At its core, Mind Hacking's utilizes the Morphogenetic field to be able to read people's hearts and minds. Delta describes his power as "touching the thoughts of other people and see into them". This allows him to be able to perceive other's thoughts and, via reading the minds of SHIFTers, learn about multiple timelines from them. With a bit more effort, Mind Hacking even allows temporary mind control, giving them full dominion of the target's actions while under their influence.
As of Zero Time Dilemma, Delta is the sole known user of this ability.