A huge flaw in Google’s wildly popular Gmail service was recently discovered that may have exposed the email addresses of every single user. According to a report from Wired, security researcher Oren Hafif found and helped Google fix a serious bug that left Gmail users’ email addresses exposed to anyone with a bit of patience. While digging up addresses would have taken quite a bit of time, the report notes that the bug had existed for years before it was fixed, and it easily could have been utilized to obtain every Gmail user’s address. According to the report, the bug would not have exposed any passwords or other sensitive data.

Until recently, anyone may have been able to assemble a list of every Gmail account in the world. All it would have taken, according to one security researcher’s analysis, was some clever tweaking of a web page’s characters and a lot of patience. Oren Hafif says that he found and helped fix a bug in Google’s Gmail service that could have been used to extract millions of Gmail addresses, if not all of them, in a matter of days or weeks. The trick would not have exposed passwords or otherwise allowed easy access to those accounts, but could have left users vulnerable to spam, phishing or password-guessing attacks. The bug may have existed for years. The exploit involved a lesser-known account-sharing feature of Gmail that allows a user to “delegate” access to their account. In November of last year, Hafif found that he could tweak the URL of a webpage that appears when a user is declined that delegated access to another user’s account. When he changed one character in that URL, the page showed him that he’d been declined access to a different address. By automating the character changes with a piece of software called DirBuster, he was able to collect 37,000 Gmail addresses in about two hours.