The extraordinary hacking spree that hit Twitter on Wednesday, leading it to briefly muzzle some of its most widely followed accounts, is drawing questions about the platform's security and resilience in the run-up to the US presidential election.
Twitter said hackers obtained control of employee credentials to hijack accounts including those of Democratic presidential candidate Joe Biden, former president Barack Obama, reality television star Kim Kardashian and tech billionaire and Tesla founder Elon Musk.
In a series of tweets, the company said: "We detected what we believe to be a co-ordinated social engineering attack by people who successfully targeted some of our employees with access to internal systems and tools."
The hackers then "used this access to take control of many highly-visible (including verified) accounts and Tweet on their behalf."
The company statements confirmed the fears of security experts that the service itself – rather than users - had been compromised.
Who did Twitter hackers hit?
Twitter's role as a critical communications platform for political candidates and public officials, including President Donald Trump, has led to fears that hackers could wreak havoc with the November 3 presidential election or otherwise compromise national security.
Adam Conner, vice president for technology policy at the Centre for American Progress, a liberal think-tank, said on Twitter: "This is bad on July 15 but would be infinitely worse on November 3rd."
Posing as celebrities and the wealthy, the hackers asked followers to send the digital currency bitcoin to a series of addresses. By evening, 400 bitcoin transfers were made worth a combined $120,000. Half of the victims had funds in US bitcoin exchanges, a quarter in Europe and a quarter in Asia, according to forensics company Elliptic.
Those transfers left a history that could help investigators identify the perpetrators of the hack. The financial damage may be limited because multiple exchanges blocked other payments after their own Twitter accounts were targeted.
The damage to Twitter's reputation may be more serious. Most troubling to some was how long the company took to stop the bad tweets.
"Twitter's response to this hack was astonishing. It's the middle of the day in San Francisco, and it takes them five hours to get a handle on the incident," said Dan Guido, CEO of security company Trail of Bits.
An even worse scenario was that the bitcoin fraud was a distraction for more serious hacking, such as harvesting the direct messages of the account holders.
Twitter said it was not yet certain what the hackers may have done beyond sending the bitcoin messages.
"We’re looking into what other malicious activity they may have conducted or information they may have accessed and will share more here as we have it," the company said.
Mass compromises of Twitter accounts via theft of employee credentials or problems with third-party applications that many users employ have occurred before.
Wednesday's hack was the worst to date. Several users with two-factor authentication - a security procedure that helps prevent break-in attempts - said they were powerless to stop it.
"If the hackers do have access to the backend of Twitter, or direct database access, there is nothing potentially stopping them from pilfering data in addition to using this tweet-scam as a distraction," said Michael Borohovski, director of software engineering at security company Synopsys.
Social media is for many politicians now the main way they communicate with the public, so Wednesday's hack left US lawmakers were wondering if it could have been worse.
"While this scheme appears financially motivated...imagine if these bad actors had a different intent to use powerful voices to spread disinformation to potentially interfere with our elections, disrupt the stock market, or upset our international relations," US Senator Ed Markey, a Democrat, said in a statement.
Frank Pallone, a Democrat who chairs the House Energy and Commerce Committee that oversees a sizeable portion of US tech policy, said in a tweet the company "needs to explain how all of these prominent accounts were hacked."