Santander is to offer all its online retail banking customers the Rapport web browser security service from Trusteer.
Trusteer is designed to prevent online fraud by protecting web communication against financial malware and phishing attacks.
"The roll out of Trusteer Secure Browsing Service to the UK retail banking customers of Santander is one of the largest free offers of online banking security by a UK bank," said Mick Paisley, head of information security at Santander.
"We are seeing the level of attacks by cybercriminals broadly increasing both in terms of volume and sophistication," he said.
According to Paisley, desktop anti-virus and anti-spyware are no longer enough.
Rapport has been rolled out to a large number of customers at Alliance and Leicester, he said, and has been very successful in protecting online banking.
"This is the main reason we are now expanding the service to all Santander customers in the UK," said Paisley.
Trusteer works directly with leading banks in the UK and around the world to identify targeted online banking attacks, block them, and remove them from your computer, he said.
"The Trusteer network includes more than 70 banks and covers more than 12 million customers," said Mickey Boodaei, chief executive at Trusteer.
"Santander's contribution to this network is extremely valuable due to its vast experience in fighting online fraud and protecting millions of customers," he said.