Jeff's Bank Recently Contacted Him to Tell Him Someone Illegally

Jeff's bank recently contacted him to tell him someone illegally accessed the bank's computer system and gained access to information about customer account numbers and PIN numbers. The bank is recommending Jeff and other customers change their account numbers and access numbers for security reasons. The bank and Jeff are victims of a

A) net crasher.
B) software pirate.
C) slammer.
D) hacker.