Data breaches may not affect share prices
but not explaining clearly what happened, making contradictory statements on what happened, fudging the dates on when it happened, not publishing a clear timeline and, worse, having the timeline contradict documented reality apparently don't help.
TalkTalk apparently believes that it doesn't matter that everything they have published is a matter of traceable public record, they can just go ahead and retconn reality by publishing any PR spiel they please.
Well apparently customers don't like that, (more importantly) investors don't like that and Joe Public thinks "What the hell are they smoking in that company ?".
That attitude does lower share prices.