The 20-year-old reality star was featured in a number of photos, including some of her and Styles on vacation in St. Bart's, where they holidayed together on a yacht in January with Styles' mother, Kendall's mom, Kris Jenner, and Ellen DeGeneres. Others snaps are candids of Styles, his family and friends.
The hackers are said to have gained access through Cox's iCloud, which led to "Anne's iCloud" briefly trending on Twitter.
Fans were initially thrilled at the prospect of new photos, but then were quick to express dismay when they learned of the source.
"Whoever hacked into Anne's iCloud should be ashamed of themselves. Show respect for the boys and their families by NOT spreading pictures," one Twitter user wrote.
Jenner and Styles, 22, have yet to officially confirm their relationship, but Selena Gomez admitted earlier this week that she was the only single one amongst her friends -- a list that included the Keeping Up With the Kardashians star. Gomez did not name her pal's beau, however.
Other celebrities have been victims of phone hacks in recent years, most notably several female stars whose nude pictures were leaked and shared widely on the internet. Jennifer Lawrence, whose photos were among those leaked at the time, called the hacks a "sex crime." Find out more of J.Law's thoughts on the incident in the video below.