It's use for protection against spoofing. People would email URLs such as
http://www.ebay.com@3478348818/verify.cgi?id=827439327432
in phishing emails. It looks like some URL at www.ebay.com, but it really contacted 209.197.123.153*. These URLs could fool even the trained eye, if it wasn't too careful.

It seems they also prevent http://3478348818/ and other uncommon forms from working now.

* – Keep in mind that 3478348818 == ((209*255+197)*255+123)*255+153.

In reply to Re^3: Login and htaccess by ikegami
in thread Login and htaccess by jacobb20

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