Shares of Twitter Inc dropped more than 4% in pre-market trading, a day after hackers gained access to the social media company's internal systems to hijack accounts of several politicians, billionaires, celebrities and companies.

Hackers infiltrated the twitter handles of U.S. presidential candidate Joe Biden, reality TV star Kim Kardashian, former U.S. President Barack Obama and billionaire Elon Musk to solicit digital currency - raising major concerns about security on the widely-used platform.

In an extraordinary step, Twitter temporarily prevented many verified accounts from publishing messages as it investigated the breach.

Twitter Chief Executive Officer Jack Dorsey said in a tweet on Wednesday that it was a "tough day" for everyone at Twitter and pledged to share "everything we can when we have a more complete understanding of exactly what happened."