Facebook, Twitter and Google have been caught snooping on messages sent across their networks, new research claims, prompting campaigners to express concerns over privacy.
The findings emerged from an experiment conducted following revelations by US security contractor Edward Snowden about government snooping on internet accounts.
Cyber-security company High-Tech Bridge set out to test the confidentiality of 50 of the biggest internet companies by using their systems to send a unique web address in private messages.
Experts at its Geneva HQ then waited to see which companies clicked on the website.
During the ten-day operation, six of the 50 companies tested were found to have opened the link.
Among the six were Facebook, Twitter, Google and discussion forum Formspring.
High-Tech Bridge chief executive Ilia Kolochenko said: ‘We found they were clicking on links that should be known only to the sender and recipient.
‘If the links are being opened, we cannot be sure that the contents of messages are not also being read.
‘All the social network sites would like to know as much as possible about our hobbies and shopping habits because the information has a commercial value.
‘The fact that only a few companies were trapped does not mean others are not monitoring their customers. They may simply be using different techniques which are more difficult to detect.’
Earlier this year scientists in Germany claimed another big computer company, Microsoft, was spying on customers using its Skype instant messaging service.
Facebook declined to comment on the latest research but said it had complex automated systems in place to combat phishing (internet identity fraud) and reduce malicious material.
Twitter also declined to comment directly but said it used robotic systems to bar spam messages from customer accounts.
A source at Google said: ‘There is nothing new here. It simply isn’t an issue.’
An independent expert explained: ‘In principle these companies should not be opening the links, but in practice they are giving a service to customers.
‘The protection provided outweighs any potential commercial gain.’
But campaigners called for stricter safeguards.
Nick Pickles, director of pressure group Big Brother Watch, said: ‘This is yet another reminder that profit comes before privacy every day for some businesses.
‘Companies such as Google and Facebook rely on capturing as much data as possible to enhance their advertising targeting.
‘They intrude on our privacy to build an ever more detailed picture of our lives.’