the matrix - Why did Bane/Smith cut himself?

In the Matrix part II and the beginning of part III the crew member who was infected by Agent Smith (Bane) cuts himself.

The female crew member in part III who brought Trinity food told her the same and speculated that they might be "VDT's".

I don't fully understand this. What are VDT's and why would Agent Smith engage in self-cutting unless he has borderline personality disorder or depression or something?

Answer

Bane's actions, in terms of cutting himself, seem to be motivated by sensory overload. Although he's experienced a range of inputs before, the sheer volume and intensity of the five human senses, especially sound and smell (something he mentioned in the first film as being one of his personal triggers) are simply overwhelming to him.

The film's original script specifically states that his reason for cutting his skin is to give him a single sensation to focus his attention on while he waits for Neo.

Bane sits hidden in the shadowed caves connecting Zion to the dock. He crouches in an alcove, both arms marked with dozens of knife cuts.

His eyes are animal wide, shifting, blinking, reacting to every sound, every smell but always returning his attention to the cut as if using it to focus his thoughts.

Finally, through the tangle of pipes and stalactites, he sees what he has been waiting for: Neo.

_{^{Matrix Reloaded: Script}}

As to what VDTs are, the simple answer is that we don't know.