There is no substitute for direct human intelligence in combating terrorist movements such as al-Qaeda. This is why the discovery of information from computer experts working for the organisation in Pakistan is such an important breakthrough, following their arrest there last month.
The plans revealed detailed preparations to attack financial targets in New York, Washington and London. Most of them were drawn up several years ago - before the 9/11 attacks in 2001 but apparently updated as recently as January this year. "What we've discovered is a collection operation as opposed to the launching of an attack," said one US official.
Significant questions are raised by this description of what was found as to whether it justifies the heightened state of alert in New York and Washington declared over the weekend and the potential panic and international attention it has involved.
Normally such reports are carefully and comprehensively checked out before being used in this way - all the more so when they are so clearly pre-operational. The information is enormously beneficial in the campaign against al-Qaeda. But it is much more doubtful whether this justifies President Bush's dramatic statement that "we are a nation in danger", as he announced on Monday the creation of a counter-terrorism centre headed by a national intelligence director.
It will be up to the US electorate to judge this issue politically in the presidential elections. Certainly the rapid release of the information in this maximal fashion has heightened tension, brought armed security police back onto the streets and reminded New Yorkers sharply that 9/11 could happen again.
This pushes the counter-terrorism issue right up the election agenda just after the Democratic convention last week, in such a way as to give Mr Bush a natural advantage as the incumbent in office. Economic and social issues on which he is weaker are displaced ahead of the Republican convention later this month.
Mr John Kerry has demanded that Congress be recalled to consider the organisational changes in the intelligence services. He says Mr Bush should respond more rapidly to terrorist threats. He criticises Mr Bush for ignoring the proposal made by the 9/11 commission that the office of counter-terrorism should be in the White House. This is conventional opposition but it does not differentiate Mr Kerry decisively from the administration at this key time.
If it emerges that security issues have been manipulated for political reasons, as reported by sections of the US media, it could be a turning point in the campaign. But security is a very tricky issue for the Democrats, indeed for any opposition party, given the genuine threats and popular fears it evokes and the possibility that a fresh attack would undermine any scepticism they mobilise about its seriousness. Mr Kerry's decision to put the war in Iraq at the centre of his campaign strategy plays into this difficulty.