Investment banks and institutional investors could spend up to $3.2bn (€3.6bn) in the next 12 months to replace the technology and systems destroyed or damaged in last week's terrorist attacks in the US.

Initial estimates from TowerGroup, a financial markets IT research firm, do not include the additional cost to securities firms which have transferred their trading functions to back-up sites in the US. Running these sites at full capacity could cost millions of dollars a day.