At the time of writing, the front page of Westpac's Web site is currently out of action, causing angst for customers around the country.
Readers contacted ZDNet Australia to report another outage that had been affecting the Westpac site since early this morning.
A spokesperson for Westpac told ZDNet Australia: "The problem is isolated to the Westpac homepage and is due to an internal systems error, which caused the page to be inaccessible. It only impacts customers who have not bookmarked the login page."
The spokesperson added: "Only 50 percent of our 400,000 customers who use the site daily were affected."
ZDNet Australia was able to confirm that at 3pm today Westpac's login page and its online banking system remain functioning.
However, according to a Crikey report earlier today, Westpac's entire online banking system had been down since 8am, including several ATMs in the south of Sydney.
"If you wait 20 minutes for customer service it will give you a secure port 43 alternative address for Westpac online which doesn't work either," Crikey reported today.
The spokesperson denied that the online banking system had been affected as Crikey and other media have reported today, and questioned if the computers used by those who reported the failure of Westpac's online banking system were functioning.
Westpac has been unable to place a notice on its Web site advising customers of the disruption to services. The spokesperson said: "Westpac apologises for the inconvenience and our staff are working hard to develop a replacement homepage."
Westpac has recently been promoting the launch of its 'new look' Web site and did alert customers last week that the site would be down for maintenance on Saturday and Sunday.
Australia's fourth largest bank has faced a series of IT and security challenges over the past 12 months. In June it experienced a system and countrywide blackout, affecting its 16,500 ATMs, EFTPOS system, online banking and several bank branches.
More recently, it has suffered a Denial of Service (DoS) attack as well as "hardware problems" that it believed scammers later attempted to exploit in a phishing campaign.
Westpac was able to pin the power outage on staff at IBM Global Services who mistakenly cut power within the bank's Ryde datacentre while providing maintenance work on a UPS (Uninterruptible Power System) device.
However a ZDNet Australia source who worked for Westpac's IT department during the June 2007 DoS attack said: "Our Information Security Group (ISG) were completely unprepared for this and didn't know the procedures that should be followed."
"We are waiting for a possible larger attack," he said, believing the hackers were probing for vulnerabilities in Westpac's IT and banking systems.