PayPal, eBay's payment service and the frequent target of fraudsters, plans to block browsers that don't include anti-phishing features from accessing its site.

Under PayPal's plan, Apple's Safari would be banned completely, while only older versions of its rivals -- Microsoft's Internet Explorer and Mozilla's Firefox -- would be barred.

"This is a good move, if [PayPal] can get away with it," said Avivah Litan, an analyst with Gartner.

PayPal spelled out the idea in a paper (download PDF) released at last week's RSA Conference. "It's critical to not only warn users about unsafe browsers, but also to disallow older and insecure browsers," said Michael Barrett, PayPal's chief information security officer, in the paper. "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."

The two features that Barrett said browsers must have to be considered safe by PayPal were an ability to block known or suspected phishing sites, and support for Extended Validation (EV) certificates. EVs, which are given to companies only after more stringent background checks than the commonplace SSL (Secure Socket Layer) certificates, are supposed to reassure users that the online site is legitimate. Browsers that support EVs typically shade the address bar green as a signal that the site is safe.

But while the current or soon-to-be-released versions of IE and Firefox support both of PayPal's must-have features, Safari includes neither.

PayPal's mentioned that before: in February, Barrett said users should steer clear of Apple's browser because it wasn't up to snuff. "Apple, unfortunately, is lagging behind what they need to do to protect their customers," Barrett said then. "Safari has got nothing in terms of security support, only SSL, that's it."

Under PayPal's plan, users running browsers lacking an anti-phishing blocking tool and support for EVs would first be only warned. Later, PayPal would block such browsers from accessing its site.

"PayPal's having to take dramatic measures," said Litan as she ticked off recent moves by the payment company and its parent, eBay, to limit fraud. "They're desperate to do something, because the [level of fraud] has even hurt their revenue picture."

Litan said that PayPal's decision was smart, but smacked of too little, too late. "They're really anxious to bring more shoppers to eBay, but consumers are staying away because of the fraud," she said. "They're right in trying to ensure the safe use of PayPal on the seller and the buyer side, but this is something they should have done a year ago."

According to Barrett's plan, older browsers such as IE3 and IE4 would be among those blocked. Conceivably, the no-longer-supported Firefox 1.x would also be kept off the site. In the paper, however, Barrett didn't call out either Firefox or Safari by name.

"I don't think it's really an issue," said Litan, referring to Safari. "How hard would it be to add those features? And I would think that most Mac users also have Firefox anyway."

PayPal did not specify a timetable when it would switch on its browser blocking, and did not reply to request for one on Friday. Apple also did not respond to an e-mail asking for comment.