Australia's St.George Bank has told technology news site ZD Net that the latest Windows update - Windows XP Service Pack 2 - will prevent customers from logging on to its online services.
The bank says the problem is caused by pop-up blocking software which is bundled with the security upgrade. According to the report, the pop-up blocker is automatically turned on, preventing customers from accessing the bank's log-in page and authentication process.
St George Bank says it may have to make changes to its Web banking interface as adoption of Windows XP Service Pack 2 becomes more widespread.
In July this year a malicious item of code that exploits unpatched security flaws in Internet Explorer to intercept online banking passwords was found in Web pop-up ads. The 'Malware' is programmed to pass on data from secure sessions between user PCs and the urls of up to 50 banking Web sites worldwide.