A new security feature was intended to protect customers but has infuriated them instead.
OCBC customers are upset that they cannot use the bank's app unless they delete other apps on their phones that are not from official app stores.
Stomp contributor Jessica was instructed to uninstall such apps as Douyin (TikTok), Alipay and Microsoft Authenticator.
She said: "OCBC's sudden drop of a new security update has failed its users, disallowing them to use the OCBC app as long as the OCBC app detects 'non-official app' in the handphone.
"However, official apps such as Microsoft Authenticator and even some anti-virus apps are being blocked.
"Even when the user uninstalls and re-downloads from the Google Play Store, there's still the same issue.
"The question now is how OCBC knows what apps we've downloaded on our phones without our permission to force users to uninstall. It is not fair for OCBC to do this suddenly.
"Many users are unable to access their OCBC app and make the necessary transactions. Take a look at their Facebook page. Many users with official apps downloaded from Google Play Store are being blocked. OCBC should not monitor their customers' phones."
Another user, Stomp contributor Andrew, said: "These apps have nothing to do with OCBC, and I've been using them for years. How can OCBC tell me what apps to use on my own phone?"
He also shared a screenshot of other unhappy customers commenting on the bank's Facebook page.
There are complaints on Reddit as well.
OCBC had announced the new security feature on Facebook on Sunday (Aug 6).
It said: "We have implemented a security feature on our OCBC Digital app to further safeguard our customers from malware.
"With this enhancement, we can detect any app that has been downloaded from unofficial app stores. Once these apps are detected, if you do not uninstall them, you will not be able to log in to our Internet Banking and/or the OCBC Digital app."
On Monday, the bank updated: "We do not monitor customers' phone activity, nor conduct surveillance on phones.
"We would like to assure our customers that our new security feature does not collect nor store any personal data from customers. This technology detects apps that are not downloaded from official app stores only when the OCBC Digital app is opened. It does not identify the owner of the device.
"All it does is to alert customers to apps that could compromise the device to malware scams.
"We apologise for any inconvenience caused. We seek your patience as this feature is aimed to safeguard customers from malware scams."
OCBC also shared a link to a police advisory on malware scams.
The director of the Association of Banks in Singapore, Mrs Ong Ai Boon, told Stomp: "Banks have been working closely with government and law enforcement authorities to fight malware scams.
"In order to detect behaviours consistent with known malware activities, a stronger security feature is being rolled out by banks. Malware scams are particularly aggressive and pose a serious threat to consumers. Malware scams are often perpetrated through apps downloaded from third-party or dubious sites.
"Together with the authorities, we have been reminding members of the public of the dangers of downloading apps from unauthorised sources that can lead to malware being installed on their mobile phones. Consumers have the responsibility to take necessary precautions and in general, will be expected to bear the losses arising from malware scams.
"Banks do not monitor customers' phone activity, nor conduct surveillance on mobile phones. We would like to assure all banking customers that this security feature does not collect nor store any personal data. The technology detects higher risk behaviours which are characteristic of known malware activities when the banking apps are opened. It does not identify the owner of the mobile phone.
"While we continue to remind consumers to remain vigilant and take all necessary precautions to guard against scams, banks have been pro-actively implementing new security measures to protect customers. In rolling out these measures, banks always strike a balance between security and convenience.
"We seek the understanding of consumers as scammers are deploying increasingly sophisticated tactics."
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This article was first published in The New Paper. Permission required for reproduction.