In a blog post, the site said that some of its customer's usernames, email addresses, phone numbers and encrypted passwords were stolen. The company says no credit card data was accessed.
Kickstarter was notified of the breach by law enforcement on Wednesday.
The company has apologized, saying it's begun strengthening security measures throughout the system. It also recommended that users change their passwords.
Kickstarter is one of dozens of crowdfunding websites that let people raise money from donors for projects. Kickstarter campaigns have included Zach Braff and Spike Lee movies, a local brewery, arts projects and business startups.
The breach comes after Target said it believes hackers infiltrated the computers of one of its vendors, and installed malicious software in Target's checkout system for its 1,800 U.S. stores. Experts believe the thieves gained access during the busy holiday season to about 40 million credit and debit card numbers. They also got the personal information - including names, email addresses, phone numbers and home addresses - of as many as 70 million customers.
The Associated Press contributed to this report.