BoA says its free SafePass service is available as an optional security feature to consumer and small business customers who use its Web banking services.

To use the service customers must register their mobile phone on the accounts overview page on the bank's Web site. Registered customers will receive a single-use six digit code in a SMS text message, which expires as soon as it is used or within ten minutes of being issued.

The code is used to authorise online transactions, such as transferring money for amounts over current limits, authorising new payees in bill pay, adding new accounts for online transfers.

BoA says the mobile authentication system provides customers with an extra layer of protection against unauthorised transactions.

SafePass can be used in addition to the bank's existing SiteKey secure log-in, where customers have to identify a small image and a brief phrase - and answer three challenge questions in order to access accounts. Customers can also use the SafePass system when logging in from a computer not recognised by SiteKey.

"Combined with SiteKey, SafePass provides online customers with a much greater level of security," says Lance Drummond, e-commerce executive for Bank of America. "We're committed to introducing features that continue to give our customers greater peace of mind when banking online."

In addition to the SMS service, BoA says it is piloting a wallet-sized card that generates a one-time password when the customer presses on a button embedded in the card.

The SafePass card will be released later this year to online brokerage clients of Banc of America Investment Services, and will be required for certain online brokerage transactions.

BoA says it plans to make the card available next year to consumer and small business customers as an optional feature that can be used in place of or in addition to the mobile phone option.