Touch attacks have a flat 70% chance to hit. The accuracy cannot be increased by an attacker's skills (e.g. Martial Arts) or status effects (e.g. Combat Clarity, but can be affected by the defender's Defense Value. The chance of hitting a target with a negative defense (whether caused by the Exposed effect, Terrifying Aura, etc) can therefore be greater than 70%.
Touch attacks are considered "close combat" attacks and as such subjects the character to defensive auras on the target and the target's dodge bonus applies.
Defilers and Dark Oppressors are currently the only classes with innate touch attacks:
Ironically, the Lich skill Death Touch is not a touch attack, but instead uses the Hand-to-Hand Combat skill tree, much like the touch spells of previous breaths.