Anders Behring Breivik has described how he "trained" for the attacks he carried out in Norway last summer using the computer game Call of Duty: Modern Warfare.

The 33-year-old said he practised his shot using a "holographic aiming device" on the war simulation game, which he said is used by armies around the world for training.

"You develop target acquisition," he said. He used a similar device during the shooting attacks that left 69 dead at a political youth camp on the island of Utøya on 22 July.

Describing the game, he said: "It consists of many hundreds of different tasks and some of these tasks can be compared with an attack, for real. That's why it's used by many armies throughout the world. It's very good for acquiring experience related to sights systems."

He added: "If you are familiar with a holographic sight, it's built up in such a way that you could have given it to your grandmother and she would have been a super marksman. It's designed to be used by anyone. In reality it requires very little training to use it in an optimal way. But of course it does help if you've practised using a simulator."

The prosecution asked Breivik if he was aware that "there are some bereaved people sitting here in the courtroom who lost children at Utøya". How do you think they are feeling, Breivik was asked. "They are probably reacting in a natural way, with disgust and horror," he said.

The court also heard that Breivik took what he called a "sabbatical" for a year between the summers of 2006 and 2007, which he devoted to playing another game, World of Warcraft (WoW), "hardcore" full time. He admitted he spent up to 16 hours every day that year playing from his bedroom in his mother's Oslo flat.

But he insisted WoW had nothing to do with the attacks he carried out last year, leaving 77 dead.

He said: "Some people like to play golf, some like to sail, I played WoW. It had nothing to do with 22 July. It's not a world you are engulfed by. It's simply a hobby."

He added: "WoW is only a fantasy game, which is not violent at all. It's just fantasy. It's a strategy game. You co-operate with a lot of others to overcome challenges. That's why you do it. It's a very social game. Half of the time you are connected in communication with others. It would be wrong to consider it an antisocial game."

Breivik said he "deserved" his sabbatical because he had worked an average of 12-14 hours every day between 2002 and 2006 on various entrepreneurial projects.

He said: "I felt I had sacrificed a lot. Because of that I felt I deserved to take one year off to do what I wanted. Especially bearing in mind the upcoming so-called suicide action … I wanted to have no remorse as to what I had missed out on."

He denied playing the game and moving back in with his mother because his business ventures, including a firm selling fake diplomas, had failed.

"If you assess what you read in media, you would think I moved back home and rented a room in my mother's house because my company had gone bankrupt," he said, claiming to have had 600-700,000 rone (£65,000-76,000) in bank accounts and 300,000KR (£32,5000) in cash, which he stashed in two safes in his bedroom at the start of his sabbatical. He only filed for bankruptcy to save on the accounting costs associated with winding down a company in a conventional way, he said.

Breivik insisted he only moved back in with his mother to save 15,000KR in monthly rent and spend more time writing his "compendium". He did not claim benefits, saying: "I have never received a single krone from any government subsidy or support because I am in principle against living off such subsidies or welfare."

He said his friends and family, particularly his mother, reacted with "shock and disbelief" when he announced he was going to play on his computer full time.

"I told her that I was going to allocate time to do what I had wanted to do. She reacted in that way, which is [a] fairly normal, healthy reaction," he said, adding: "It would have been quite abnormal if she had just said: 'Oh that's great, go ahead.' I couldn't tell her I was taking a sabbatical because I was going to blow myself up in five years' time. I played on the idea that: 'Ooh, I've become addicted to games.' That was my primary cover."

It was a convenient "cover" and allowed him to isolate himself and concentrate on his forthcoming "operation". But he insisted repeatedly he was not a loner and had been out and about in the months leading up to the attacks in July last year.

Breivik was also asked about his membership of the masons. He said he joined because it was a "Christian organisation which has protected many European traditions" but said he was not an active member.

It was a "hobby", he said, claiming to have only attended "about five" meetings. It was another "militant nationalist" who suggested he join, he claimed.