Mirror.co.uk reports that Gaga's Britain website was hacked by US cyber attackers SwagSec, prompting her record label Universal to take urgent action.
"She's upset and hopes police get to the bottom of how this was allowed to happen," said a source.
The cyber attack happened on June 27 but those responsible didn't make the information public until this week.
The hackers, who also issued a death threat against the singer, bizarrely branded her homophobic.
"The hackers took a content database dump from ladygaga.co.uk and a section of email, first name and last name records were accessed. There were no passwords or financial information taken," said a spokesperson from Universal label.
"We take this very seriously and have put in place additional measures to protect personally identifiable information. All those affected have been advised," the source added.
SwagSec have also targeted other Universal artists recently including Amy Winehouse and Justin Bieber.