PayPal, the online payments business of electronic auction house eBay, says it will block people from accessing its site with older browser technology that leaves users exposed to security risks.
The firm says it will warn customers using unsafe, usually old, browsers when they log in to the site before blocking them if necessary.
In a white paper the eBay subsidiary claims "there is a significant set of users who use very old and vulnerable browsers, such as Microsoft's Internet Explorer 4 or even IE 3".
PayPal says "letting users view the PayPal site on one of these browsers is equal to a car manufacturer allowing drivers to buy one of their vehicles without seatbelts".
PayPal, a popular target for phishers, is championing the uptake of Extended Validation SSL Certificates, where the address bar is highlighted in green when a Web site is deemed legitimate.
Newer versions of Internet Explorer and Firefox support this technology but Safari, Apple's browser, does not.
Says PayPal: "These newer browsers make it much easier for users to determine whether or not they're on the site that they thought they were visiting."
The popularity of phishing seems to be on the rise with UK payments association Apacs reporting a 200% jump in the number of attacks in the first quarter of 2008.
There were 10,235 phishing incidents targeted at UK banks and building societies in the first quarter of this year, compared to 3394 in the same period the previous year.