I want to make sure I have Tar Pit understood correctly.
If the attack is successful, you "do 1+net hits damage to the icon". I assume this damage is resisted as normal, even though the language is different than Data Spike. Otherwise Tar Pit is really destructive against hard targets, especially if you're in a Sleaze posture.
You also "reduce their Data Processing rating by the same amount". I'm not sure whether this amount is the value before the resistance test or after it, assuming there was one.
The DP attribute of the victim of a Tar Pit attack recovers at a rate of 1 per round. When does this recovery take place? Timing is important here. Since a device with DP of 0 cannot perform any matrix actions, it has to be assumed this recovery happens after the victim's turn, otherwise their DP would never be 0. It's never mentioned when this happens though.