In an effort to improve security, Google is inviting hackers to find problems in the Chrome operating system.

Anyone who finds holes in the company’s security will be rewarded with a part of a $2.7 million reward.

Google has run this contest for four years in a row and rewards for a hack range between $110,000 and $150,000.

The first two years, hackers found problems. But last year, no one was able to breach Chrome’s security, despite the company offering a $3.1 million bounty.