it's not alleged, it really did happen.
the 23 year old 'bomber' is steve's (the guitarist) neighbor and there is (was) an on-going dispute over noise levels (except that steve hasnt been home in the past 3 months on tour and all). anyway, the guy through a bomb that hit the front door, but it didnt go off. steve picked it up and stuck it in the freezer for evidence. the guy throws another one that explodes, so steve calls the cops. he takes the bomb out of the freezer to show them the one that didnt explode, handed it to the security guard, and 30 seconds later the thing explodes, injuring steve, a cop, and severely injuring the security guard. steve suffered a concussion and fluid in his ear and he has to take a break for touring. (took that info from the ul site).
im not a big fan of UL, but i did see the first show of the tour and they played pretty good and the crowd was really into it.