Twitter has warned a number of users that their profiles may have been the target of state-sponsored hacking.
Over 20 users of the popular social network have been listed as receiving a letter from Twitter saying that the accounts were part of a "small amount" of profiles singled out by an unnamed state actor.
The notes said: "We believe that these actors (possibly associated with a government) may have been trying to obtain information such as email addresses, IP addresses and/or phone numbers.
"At this time, we have no evidence they obtained your account information, but we're actively investigating this matter. We wish we had more we could share, but we don't have any additional information we can provide at this time.
"It's possible your account may not have been an intended target of the suspected activity, but we wanted to alert you as soon as possible."
Many of the affected users regularly tweet about cyber security, privacy and cryptography, including information security non-profit Coldhak, privacy and security researcher Runa Sandvik, and Anne Roth, a researcher at the German parliamentary inquiry on mass surveillance.
Twitter advised users to download the Tor browser to stay protected online but, as many pointed out, the social network has blocked accounts that access its service via Tor in the past.
Twitter suggests I use Tor to protect my online identity, yet frequently blocks accounts accessed over Tor. pic.twitter.com/5ChKERPscC— Runa A. Sandvik (@runasand) December 11, 2015
Twitter now joins Google and Facebook in offering nation-state snooping warnings. Google has provided this service since 2012, while Facebook announced plans to do so earlier this year.
Eric Grosse, vice president of Google's security engineering department, explained at the time how to react if you receive a snooping notification.
"There are some things you should do immediately: create a unique password that has a good mix of capital and lowercase letters, as well punctuation marks and numbers; enable two-step verification as additional security; and update your browser, operating system, plugins and document editors," he said.
"We decided to show this additional warning if we have a strong suspicion that an attack could be government-sponsored. We do this because these types of attacks tend to be more advanced and dangerous than others, and we strongly encourage affected people to take the actions necessary to secure all of their online accounts," wrote Alex Stamos, chief security officer at Facebook, at the time.
The warnings come amid an increased focus on cyber security and government hacking. Surveillance legislation in the US and the UK is now being debated that would enhance the snooping powers of spy agencies and police services.
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