(MESSAGE EDITED TO REFLECT INFORMATION FOUND)
Don't remember the episode, but there are those scenes where someone (Luthor?) talks to Superman in high-frequency and then sends those paint missiles towards Jimmy and Lois as a warning. I remember they were tagged with a mechanical bug (Clark captures it and sees that it is mechanical, while the guys that command this bug complain that it is non-responsive).
Anyone can pinpoint the episode and confirm if it was Luthor?
EDIT: Okay, found the information. It's Martin Snell (Intergang's lawyer) in "Church of Metropolis". From
http://www.redboots.net/Episodes/season_2a.htm :
Clark then hears a high-frequency message from Martin Snell, Intergang's lawyer. When Superman confronts Snell, Snell demonstrates that Lois is vulnerable by sending a paint missile at her. Superman catches the missile, but Snell then tells Superman that if he doesn't stay away from the Southside, Lois is dead.
malu