Twitter has notified 10,000 users that their email addresses and phone numbers may have been exposed due to a bug in the website's password recovery feature.
The incident happened over the course of 24 hours on an unspecified day last week, but the company alerted affected users on Wednesday.
"Any user that we find to have exploited the bug to access another account’s information will be permanently suspended, and we will also be engaging law enforcement as appropriate so they may conduct a thorough investigation and bring charges as warranted," Twitter said in a blog post.
It's not uncommon for website features to be abused to expose users' identifying information, such as email addresses and phone numbers. In 2012, Facebook imposed a limit on phone number searches through its mobile website, because a security hole could have allowed attackers to search through phone numbers sequentially and match them to existing users.
Other leaks of personal information can be hard for users to detect. For example, recent data breaches at online dating websites Adult Friend Finder and Ashley Madison understandably enraged a lot of users whose spouses, partners or friends did not know that they had accounts there.
However, many of those users didn't know that ,even before hackers broke into those websites, anyone could have checked if their email addresses were registered through the sites' password recovery systems.
Users should not count on websites to shield their affiliations with those services, because leaks of registration information are common. From a security perspective, users valuing their privacy should take advantage of tools available to protect their accounts from possible hijacking, for example by enabling two-factor authentication when offered.
Twitter offers a feature called "login verification" that requires users to supply one-time-use codes sent to their phones in addition to their passwords when they authenticate. In addition, Twitter offers the option to require additional information, such as the user's email address or phone number, when initiating password resets. This option can be found on the account's security and privacy settings page. Without it, initiating a password reset requires only the account's username.
Twitter users should also consider using a strong password or passphrase of 10 or more characters, periodically reviewing their accounts' login histories, and checking their account application tabs and revoking access to any applications that are no longer used.