Twitter seems to be secretly keeping hold of direct messages between users long after they were deleted, a security researcher has discovered.

Delhi-based researcher Karan Saini discovered long-ago deleted messages when he downloaded an archive of his data from Twitter, including messages sent to accounts that have since been deactivated.

"DMs are never 'deleted' – rather only witheld from appearing in the UI," Saini wrote on Twitter. "The archive geature lets you view these DMs, as well as any others with now suspended, or deactivated users."

In a follow-up tweet, he added: "I submitted the report for this to Twitter in January of 2018, and at the time, the team accepted the residual implications of the issue."

The issue raises serious privacy concerns for Twitter users, though Mr Saini noted that it is not a security flaw, rather a "functional bug".

11 useful Twitter features you might not know about Show all 11 1 /11 11 useful Twitter features you might not know about 11 useful Twitter features you might not know about Turn on Night Mode Twitter’s dark blue Night Mode is a lot easier on your eyes than its regular, vibrant theme. On the site, you can enable it by clicking your profile photo (on the right-hand side of the bar at the top of the screen) and selecting Night Mode. On Android and iOS, you need to tap your profile picture at the top of the screen and select Night Mode. 11 useful Twitter features you might not know about Lengthen your tweets A “small group” of users are no longer restricted by Twitter’s 140-character tweet limit. Even if you’re not a chosen one, you can double your limit to 280 characters on desktop by downloading the Tampermonkey plugin, going to https://gist.github.com/Prof9/c16fc4997e0ef5b22a15c43edd7f5f49, clicking Raw and then Install. 11 useful Twitter features you might not know about Improve search Twitter’s regular search tool can be a little messy, but Advanced Search makes it much easier for you to find specific things. Go to https://twitter.com/search-advanced and filter your search by word, hashtag, exact phrase, location, date and account. 11 useful Twitter features you might not know about Disable read receipts Like WhatsApp and Facebook Messenger, Twitter’s direct messaging service shows you when your messages have been seen by the person you sent them to. You can disable read receipts though. On Android, iOS and the site, go to Settings and Privacy, click on Privacy and Safety and disable read receipts. 11 useful Twitter features you might not know about Monitor your tweets Retweets and Likes only form part of the story, as far as tweet engagement is concerned. You can view a lot more information about how people have reacted to your updates, including the number of times they’ve been seen and the number of times people have interacted with them. Just open your tweets and hit the View Tweet Activity button. 11 useful Twitter features you might not know about Trim the fat If you feel like you’re drowning in push notifications, you can cut down the number you receive from Twitter by going to Settings, Notifications, Push Notifications and deselecting the types of notifications you wouldn’t like to receive. You can also enable sleep settings, which allow you to switch off all mobile updates during certain hours of the day. On the site, go to Settings, Mobile and select your hours. 11 useful Twitter features you might not know about Save data You can stop videos from playing automatically on desktop and the Twitter app. On the site, you can do this by going to Settings, Account, Video Tweets and unchecking Video Autoplay. On both the Android and iOS versions of the app, go to Settings, General, Data Usage, Video Autoplay, and choose between Mobile data & Wi-Fi, Wi-Fi Only, and Never. 11 useful Twitter features you might not know about Save even more data You can save even more data and completely transform your timeline in the process by disabling images. Just go to Settings, Data Usage and uncheck the Image Previews box. 11 useful Twitter features you might not know about Customise your profile Editing your Twitter profile is really straightforward, just go to your profile and click the large Edit Profile button. However, there’s one customisation option that’s easy to miss. As well as your name, bio and profile photos, you can change your colour scheme. The option is only available on the Twitter site, and is sandwiched between the Website and Birthday sections. 11 useful Twitter features you might not know about Browse properly One of the Twitter app’s most annoying features is its in-app browser, which links automatically open up in. You can sacrifice it for your favourite mobile browser by going to Settings, Display and Sound and unchecking the Use In-App Browser box. 11 useful Twitter features you might not know about Subscribe to tweets You can set up alerts that let you know whenever a certain account tweets, but it’s a two-stage process. First, on the app, go to Settings, Notifications, Push Notifications, Tweets and turn the toggle button on. Then open the profile page of the account you want to receive notifications from, tap the Bell icon next to the Following button and choose between All Tweets, Only Live Video and Off.

Twitter's privacy policy states that anyone who deactivates their account will have their data deleted after a 30-day grace period.

"For up to 30 days after deactivation it is still possible to restore your Twitter account if it was accidentally or wrongfully deactivated," the policy states.

Twitter's terms state that log data – which includes information like IP address, browser type and operating system – is kept for a maximum of 18 months, though this does not encompass private data like direct messages.

A Twitter spokesperson was not immediately available for comment.