Natalie Portman and Glee actress Dianna Agron are among the Hollywood elite who have been targeted by a group of hackers.
According to celebrity website TMZ, more than 100 famous names have had their contact details stolen, including telephone numbers and email addresses.
Other celebrities have had private photographs and videos taken.
Investigators from the FBI are understood to be looking into how the hackers managed to access the information, which includes that of actress Scarlett Johansson.