According to a document leaked by Edward Snowden, the National Security Agency (NSA) collects up to 250 million online address books each year.
The NSA document was leaked to the Washington Post and shows a collection of contact lists from both foreign and US email and instant message accounts.
Scrutinizing such lists allows the NSA to find hidden connections between people of interest to them, it says.
The web firms involved said that they did not give direct access to the NSA.
During a single day last year, the NSA collected 444,743 email address books from Yahoo, 105,068 from Hotmail, 82,857 from Facebook and 33,697 from Gmail, according to the alleged internal NSA Powerpoint presentation.
Another 22,881 address books were harvested from unspecified providers, according to the Washington Post.
In response to earlier allegations, Yahoo said that it would begin to encrypt email connections from next year. Meanwhile Facebook called for greater government transparency about data collection and Microsoft said the revelations raised “significant concerns”.
The data collection, which the paper says takes place overseas, happens when users log in, compose a message or sync devices.
According to the leaked document, the information is collected at least 18 key access points controlled by telecommunication companies based outside the US.
Because American web communications can flow outside of the country, the contact lists of US citizens also cross the international collection points, known as Sigads (Signals Intelligence Activity Designators).
This is particularly significant because President Barack Obama has previously said that US citizens were not targeted by the surveillance, which he said struck “the right balance” between security and privacy.
Address books include names and email addresses but can also include telephone numbers, home addresses, and business and family information.
Many web-based email services generate contact lists automatically once an email has been sent. These lists allow users to write emails more quickly by providing an auto-complete suggestion.
For an intelligence analyst, access to such data would allow them to reconstruct a network of who knows whom among criminals and terrorists.
Previous Edward Snowden allegations have suggested large-scale NSA spying and attempts to weaken internet encryption.
The NSA said that such surveillance is used to combat terrorism, drug smuggling and human trafficking among other crimes.
It has always maintained it has no interest in the personal information of ordinary Americans.
NSA director general Keith Alexander has defended the bulk collection of internet communications, saying that counter-terrorism and serious crime-fighting requires “the haystack to find the needle”.
[youtube vpkkQ-uX04w]
