New Delhi: Close to two decades since the 9/11 attacks, the surveillance system built by the US spy agencies has become so sophisticated that they can access every single detail about you, irrespective of your location, whistleblower Edward Snowden says in his much-awaited memoir "Permanent Record" released this week.

Snowden, who served as an officer of the Central Intelligence Agency (CIA) and worked as a contractor for the National Security Agency (NSA), rocked the world in 2013 after he revealed that the US was secretly building a way to collect the data of every person in the world, including phone calls, text messages and email.

"No matter the place, no matter the time, and no matter what you do, your life has now become an open book," Snowden wrote in his memoir published by Macmillan.

The 339-page book details how the change in the American espionage system - from targeted surveillance of individuals to mass surveillance - took effect. The title of the book refers to the system of storing data permanently and the dangers associated with it.

The intelligence community in the US sought to take advantage of the fact that about 20 years ago hardly any online communications were encrypted. And what prompted them to exploit this vulnerability was the failure to prevent the 9/11 attacks.

The book is as much about the unethical practices of spy agencies, as it is about Snowden's meteoric rise within the CIA and NSA, and the struggles with his conscience. It is also about his greatest regrets and the final triumphs.

"September 12 (the day after the September 11 attack of 2001) was the first day of a new era, which America faced with a unified resolve, strengthened by a revived sense of patriotism and the goodwill and sympathy of the world.

"In retrospect, my country could have done so much with this opportunity... Instead, it went to war.

"The greatest regret of my life is my reflexive, unquestioning support for that decision," Snowden, who got his first top-secret clearance from the NSA when he was just a 22-year-old, said.

It was the love for his country that led Snowden to join the CIA and it was again "apolitical patriotism", the principles enshrined in the US Constitution that guided him to make the shocking disclosure a year before he turned 30.

And he believes that six years since then, the Internet has become much more secure, thanks to the global recognition of the need for encrypted tools and apps.

Snowden himself has been involved with the design and creation of some of these through his work heading the Freedom of the Press Foundation, a non-profit organisation dedicated to protecting and empowering public-interest journalism.

Six years since he had made the disclosure, knowing fully well the trouble he and all those connected to him would face, Snowden is living in exile in Moscow. He frequently refers to the US as "my country" in the memoir.

He got married two years ago to the person he first met many years ago online (through a site called HotOrNot.com that originated in the pre-Facebook era) and now spends time just like many of us do - in front of the computer to read, write and interact with people.

But whenever he goes out with his partner Lindsay Mills for a Bolshoi Theatre show, or just for a stroll, he tries to change his appearance a bit to avoid unnecessary public attention.

Exile, for Snowden, is an endless layover.