Security researcher Ibrahim Balic found that it was possible to upload entire lists of generated phone numbers through Twitter's contacts upload feature, reports TechCrunch.
"If you upload your phone number, it fetches user data in return," he was quoted as saying.
Most of the users were in countries like Israel, Turkey, Iran, Greece, Armenia, France and Germany.
In one case, TechCrunch was able to identify a senior Israeli politician using their matched phone number.
Over a two-month period, Balic began alerting users directly and when Twitter came to know, the micro-blogging platform blocked his efforts on December 20.
Balic had created a WhatsApp group to alert users.
He generated more than two billion phone numbers, one after the other, then randomized the numbers, and uploaded them to Twitter through the Android app.
The bug did not exist in the web-based upload feature.
It's not yet confirmed if Balic's efforts are related to a Twitter statement last week which admitted a malicious code was inserted into its app by a bad actor that could have compromised several Android users' information worldwide, including in India.
The vulnerability within Twitter for Android could allow the bad actor to see non-public account information or to control your account (send Tweets or Direct Messages).
Balic is previously known for identifying a security flaw breach that affected Apple's developer center in 2013.
A Twitter spokesperson said the company takes these reports seriously and are actively investigating to ensure this bug can't be exploited again.
Twitter has faced several vulnerabilities on its platform in the recent past.
In May, Twitter disclosed a bug that shared some iOS users' data with an unnamed partner, even if the user did not opt to share data. The bug affected Twitter's iOS user base and they were notified about the issue.
In February, a bug in Twitter exposed private tweets of some Android users for over five years when they made changes in their settings, like changing the email address linked to their accounts.
In a huge data breach last year, the micro-blogging platform alerted all users to change their password after it discovered a bug that stored passwords in plain text in an internal system.
( With inputs from IANS )