I was a little taken aback. Miffed, indeed. Ed Curran was a former spook with the FBI who had worked in counter-intelligence with Robert Hanssen and was speculating about the signs of incipient treachery that might have been interpreted earlier with the benefit of hindsight. "Anyone who read Kim Philby at 14," he declared to CNN, "has a few screws loose anyway."

Well, I have to confess that I am one of those, and still in possession of most of my marbles. Nor am I a Russian spy - not that I would tell you if I was.

But I do remember the passing frisson of excitement that Philby's story represented at that age and I could see what Hanssen meant when he wrote to his spymaster that that same reading had inspired him to do what he did.

American commentators on the case this week have been confused by the reference, pointing to the obvious difference between Philby, a committed communist who spied for ideological reasons, and Hanssen's clearly mercenary motivation. $1.4 million is no small beer. And Hanssen, by all accounts, is deeply conservative.

Marvin Ott, of the National War College, is closer to the mark. Hanssen, he argued was fascinated by the same question that fascinated me when I read Philby - "Could he get away with it?" Philby the spy, not Philby the communist, was the clue. The money, I am willing to wager, we will find to have been the icing on the cake.

Ernie Rizzo, a former FBI colleague, told the New York Times: "If Hanssen did what they say he did then he didn't do it for money. When you're into that super-spy stuff, you just get into it so deeply and then get lost in it. It couldn't have been the money for him. It was the spy game."

To be successful he needed the temperament and the technique. And the FBI would give its brilliant student all the latter.

Littered through the 100 pages of his correspondence with the KGB, released by the FBI this week as the basis for its case for the death penalty, and which itself represents a remarkable intelligence coup, comes clearly Hanssen's obsession with spycraft. In a very real sense Hanssen ran his Russian spymasters, not the other way round, preserving his anonymity from his masters to the end. He set the rules, like refusing to meet abroad, or rejecting alternative drop sites. "I am open to commo (communications) suggestions but want no specialised tradecraft," he wrote in 1985 in his initial letter. And that first step, carefully planned, was entirely his, a letter within a letter sent to a junior KGB man with instructions to pass it, still sealed, to spymaster Viktor Cherkashin, a man Hanssen knew, by reputation inside the FBI, would not fumble the pass.

In his letters it is Hanssen who describes signals to be used, code words, payment methods, the wording of an advertisement in the Washington Times that will trigger a response from him: "Dodge '71 - Diplomat needs engine work, $1,000. Phone . . ."

After more suggestions that he should work their way, in 1987, he wrote: "No. I have decided it must be on my original terms or not at all . . . If my terms are unacceptable then place no signs and withdraw my contact."

In 1988 he reiterated his fears: "My security concerns may seem excessive to you . . . I am much safer if you know little about me." Later he would speculate about the possibility of facing the death penalty.

At other times he flattered and paid tribute to the Russians' own methods, much as a spymaster will routinely flatter his agent in the field.

The letters reflect too his disdain for his country. In June last year he wrote: "The US can be errantly likened to a powerfully built but retarded child, potentially dangerous but young, immature, and easily manipulated. But don't be fooled by that appearance. It is one which can also turn ingenious quickly, like an idiot savant . . ."

And there are clues to Hanssen's temperament in both the facts of his life and the testimony of co-workers. A brilliant student, the son of a policeman who worked some of his career in criminal intelligence-gathering, Hanssen was recruited into the FBI in 1972 from training, moving immediately into a unit that would set him apart from many fellow officers, investigating internal corruption. It is a job many policemen find very difficult.

BUT success there saw him fast-tracked into the FBI's counterintelligence unit, again a job apart, where he worked for the rest of his career, rising through important command posts in the ultra-sensitive New York office, with its particular focus on Russian penetration, to end acting as liaison with the State Department. Ed Curran spoke of an "aloofness", a lack of empathy, and "old-world demeanour" that neighbours also observed in the 56-year-old man who, unlike his wife, did not socialise easily. Another former agent, John Gaskill, described him as "a towering intellect". Yet another colleague describes him as someone with a brilliant gift for quiz shows but little for human relationships. And his membership of Opus Dei is fascinating. Here is an organisation whose secretive elitism would flatter his ego as one of the chosen few. It would reinforce that sense of apartness and superiority and perhaps provide an internal rationale. For a man who serves no king but Jesus may be a man who sees little reason for loyalty to any particular state.

Truly a character worthy of Le Carre.

And for the FBI now a period of soul searching as a thorough review of security and damage assessment is carried out by a former head of the agency. Hanssen had access to a staggering wealth of material, not only from his own agency but the CIA and the National Security Agency. Undoing the damage will probably take years.

Not least, the question will be asked whether the organisation's refusal to put its employees, particularly those in the most sensitive posts, through lie detector tests was sensible.