The bank has begun issuing Vasco's Digipass GO3 two factor digital authentication tokens to users of the CitiBusiness Internet banking service. The token generates a single-use password for accessing online applications.

Citi says the token substantially reduces the risk of unauthorised access to customers' accounts through key logging and spyware techniques.

By early summer, business customers who use the Internet for cash management services and other financial transactions will be required to sign on using the token-generated security password in order to complete transactions. If they do not have the token with them, customers will still be able to sign on to view limited account information, but will be unable to perform transactions.

Jorge Bermudez, chief executive officer of Citigroup's commercial business group, says: "By offering this technology to our clients, our message is clear: We will continue to look for innovative ways to enhance protection for our clients and their financial assets. While this initiative involves a sizeable technology investment on our part, it is indicative of the type of effort Citigroup makes every day to keep our clients assets safe."