The mainland attack has forced companies to think anew about where they might be vulnerable. Corporate America is now having to scramble to improve its security both domestically and overseas. The measures many large companies are putting in place may change aspects of corporate life for years to come.
Mr Brandon said the immediate question asked by many multinationals was "should we start pulling people home". Smith Brandon , his consultancy, has taken calls from clients with operations in the Middle East, Asia, Africa and Latin America, all expressing similar concerns.
For now, experts are not advising companies to go for mass evacuations of employees, but there are some exceptions.
Richard Fenning, chief operating officer of Control Risks, one of the largest corporate security companies, said: "We're saying that the few organisations with operations in Afghanistan should get out. In Pakistan and Yemen, what we're saying is that it would be wise at this stage to evacuate dependents."
Within the US, Control Risks expects increased security around office buildings, and several companies confirmed they had taken such measures.
Procter & Gamble, the largest US household goods group, said security was tightened around the company yesterday, with employees advised to display their identification badges at all times and to be vigilant.
P&G also told employees around the world on Tuesday that they should not fly until the Federal Aviation Administration had given the all-clear, a spokeswoman said.
Texaco, the US oil com pany which is used to operating in tense parts of the globe, said it was in a "heightened state of security" in all its operations, overseas and within the US.
Some industries have issued specific advice to employees in sensitive jobs. The Air Line Pilots Association advised its members to stay away from airports and to wear civilian clothes for fear of further attacks.
As airlines prepared to recommence flights yesterday, many predicted that business travel would never be the same again. "Corporate America lives by the aeroplane, and on a continent-sized economy it is an important tool," said Mr Fenning.
That reliance on air travel might now have to change. "Regardless of what happens in the next few days, people are going to have to get used to a huge amount of inconvenience associated with air travel."
Such fears are supported by an instant survey conducted by the Business Travel Coalition. The trade group contacted almost 200 corporate travel managers, of which 62 per cent said their companies had suspended travel for the rest of the week.
Almost all expected a significant increase in airport security, and 56 per cent said their confidence in aviation security was seriously eroded.
Mr Brandon said that the issue of pulling US staff out of foreign postings would depend on whether any embassies around the world were shut.
After the initial shock, he and other consultants are seeing an increased demand from corporate clients for "actionable intelligence" - up-to-the-minute advice on the changing political climate in various markets to allow them to decide whether to stay or go.
US companies are not starting such efforts from scratch. Most have well-rehearsed security measures in place, and the increased awareness of external and internal threats has fuelled strong growth in the corporate security industry in the past decade.