Hackers stole the passwords of a huge number of users.
Tips
usage
黑客 is the everyday mainland word for a hacker. 骇客 is the usual word in Taiwan, and on the mainland it is sometimes kept for the malicious "cracker" who breaks into systems. Both imitate the sound of English "hacker", and 骇 "to frighten" adds menace.
In Pop Culture
骇客帝国Hàikè dìguó
The Matrix
The Matrix (1999), the Wachowskis' science-fiction film; its mainland title is more often written 黑客帝国.