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Opera

The strongest alternative to IE and Mozilla on most operating systems is Opera.

Opera has a unique approach to its user-agent string. The basic user-agent string has the following format:

Opera/

AppVersion

(

;

Security

)[

Language

]

Using Opera 7.54 on a Windows XP computer, the user-agent string is the following:

Opera/7.54 (Windows NT 5.1; U) [en]

To its credit, Opera came up with a unique user-agent string to correctly (and simply) identify its Web

browser. The problem comes with another unique browser feature: the capability to disguise itself as

another browser.

Just by using a menu, Opera users can choose to identify the browser as Opera or as one of the various

versions of Internet Explorer and Mozilla, including older Netscape versions. To do this, Opera changes

the user-agent string it reports, as well as adapts some of its other features (including values of the

nav-

igator

object) to try to emulate the other browsers. However, it doesn’t fully emulate the browsers it

disguises itself as, so it is still important to determine if a browser is actually Opera in disguise.

When Opera is being disguised as Mozilla 5.0, it returns a user-agent string that looks like this:

Mozilla/5.0 (Windows NT 5.1; U) Opera 7.54

As you can see, the application name has changed to Mozilla, and the version is now 5.0, just like

Mozilla’s user-agent string. Note that the string

“Opera 7.54”

is added towards the end, which still

allows identification of the browser as Opera.

If Opera is disguised as Mozilla 4.78, the user-agent string looks like the following:

Mozilla/4.78 (Windows NT 5.1; U) Opera 7.54

This isn’t too different from the Mozilla 5.0 identification because only the Mozilla version has changed.

The same is true for Mozilla 3.0, which looks like this:

Mozilla/3.0 (Windows NT 5.1; U) Opera 7.54

If Opera is disguised as IE 6.0, the user-agent string changes to this:

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1) Opera 7.54

Before version 7.0, Opera could interpret the meaning of Windows operating system

strings. For example, Windows NT 5.1 actually means Windows XP, so in Opera 6.0,

the user agent included Windows XP instead of Windows NT 5.1. In an effort to be

more standards-compliant, version 7.0 started including the officially reported oper-

ating system version instead of an interpreted one.

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