Twitter losing cat and mouse game with pro-Assad Syrian hackers who 'blew up the White House'

The Syrian Electronic Army is now on its seventh Twitter account after the previous six were shut down

Twitter's security staff seem to be fighting a losing battle against Syria-based pro-Assad hackers, whose reach has now spread to US financial markets.

One hundred and thirty-six billion dollars (£89 billion) was wiped from the top 500 US stock exchange listed companies on Tuesday after the group - which call itself the Syria Electronic Army - hacked the Associated Press news agency's Twitter account and posted an update claiming that there had been an explosion at the White House and that President Barack Obama had been injured.

The AP attack was the most recent in a long line of hacks by the SEA on Twitter accounts of large Western organisations and figures, including the BBC, Fifa president Sepp Blatter and American television network CBS.

Graham Cluley, of internet security firm Sophos, told The Times: “The SEA has the potential to be very dangerous because they have the ability to hack into accounts followed by many millions of people, although most of what they have done so far appears to be more mischievous than dangerous.”

The SEA has already had several of its own Twitter accounts suspended by the micro-blogging site, only for them to reappear under different guises. As of today, the group seemed to be tweeting as @SEA_Official7.

On its website the group said it is against the "campaigns led by the Arab media and Western on our Republic by broadcasting fabricated news about what is happening in Syria".

Though the SEA has most recently targetted prominent Twitter accounts over the last few weeks, the group began by defacing websites of all sorts, according to Helmi Norman, an expert from Toronto University, who has been tracking them for years.

The group's domain names were apparently registered by the Syrian Computer Society, which was headed in the 1990s by Bashar al-Assad before he became president.

However, the SEA retweeted a tweet from rival hacking collective Anonymous this week that said: "By the way #SEA is not supported or funded by the government of Syria."

Mr Cluley told The Times that it is hard to know who is behind the attacks, but warned that if they were really coming from the Syrian regime, "they could do a lot more damage".

Twitter have been approached for comment.