The social media giant Twitter acknowledged that it had become the latest victim in a number of cyber-attacks against media companies, saying hackers may have gained access to information on 250,000 of its more than 200 million active users.

The company said in a blog post on Friday it detected attempts to gain access to its user data earlier in the week. It shut down one attack moments after it was detected.

But Twitter discovered that the attackers may have stolen user names, email addresses and encrypted passwords belonging to 250,000 users they describe as “a very small percentage of our users”. Nonetheless, the company reset the pilfered passwords and sent emails advising the affected users.

The online attack comes on the heels of recent hacks into the computer systems of U.S. media and technology companies, including The New York Times and The Wall Street Journal. Both American newspapers reported this week that their computer systems had been infiltrated by China-based hackers, likely to monitor media coverage the Chinese government deems important.

Bob Lord, Twitter’s director of information security, said in the blog that the attack “was not the work of amateurs, and we do not believe it was an isolated incident”.