Virgin Money, TSB and Nationwide are missing security protections, potentially leaving "open doors" for scammers, it has been claimed.
Which? tested customer-facing security systems of 13 current account providers from September to November 2022, with help from security experts at Red Maple Technologies.
Account providers were scored by looking at their processes for login, navigation and logout, account management and encryption - for both their online banking security and app security.
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Virgin Money was scored the lowest overall for online and app banking in the research. A spokesperson for Virgin Money said: "The safety and security of our banking services is our top priority, and we are continually monitoring, assessing and improving our security controls.
"A number of the points raised in this research relate to decisions we've taken to enhance the digital user experience while ensuring our robust, multi-layered controls remain in place to protect customers' accounts."
Which? said it also had some concerns over TSB, which received the second lowest score for its app in the study. A spokesperson for TSB said: "We continue to invest in our online and mobile services - and work with globally leading tech firms to deliver both security and accessibility to our customers. TSB also tracks well across the industry on fraud prevention and we are the only bank that protects its customers with a guarantee to return their money should they ever fall victim to fraud."
Nationwide Building Society was given the second lowest score for online banking security. A spokesperson for Nationwide said: "Nationwide takes the security of its members and their money very seriously.
"We are never complacent and conduct regular testing of our systems to ensure that we maintain an appropriate level of protection, whilst ensuring a positive user experience. We will take the points raised by Which? on board as we continue to evolve our digital services."
Meanwhile, Which? said Starling Bank was placed top for online banking security. Its top scorer for online banking security last year, HSBC UK, also performed well this year. HSBC followed closely behind Starling for online banking, while its app had the highest score.
Which? said the banks included in the research also have behind-the-scenes systems that the consumer group and Red Maple Technologies were not able to test. In general, the consumer champion said it wants improvements that would see weak passwords blocked and it also believes that sensitive data should not be sent via text messages as these can be intercepted.
If the worst happens and people do fall victim to remote banking fraud, in many cases they will be entitled to a refund from their bank.
Sam Richardson, Which? Money deputy editor, said: "Banks should not be leaving these open doors for scammers to exploit and must up their game to protect their customers properly.
"By making improvements, such as blocking weak passwords, banks can take an important step in preventing unscrupulous fraudsters from attempting to steal money and personal data from consumers."
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