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Faking Browser IDs


I used to rely on The Proxomitron to completely override the identity Opera sent to web sites to versions that didn't mention Opera.

With the release of Opera 8, that functionality is now built-in to Opera. The "ua.ini" file allows you to set on a per-site basis, which identity Opera should use when visiting that site, including identities that hide the fact it's Opera visiting!

The file is a plain text file, editable by Notepad (or similar) and has a simple format, so it's quite practical for you to add your own entries.

It is stored in your profile folder. Select About Opera from the Help menu. The "Opera directory" is your profile folder. If you can't find a ua.ini file in that folder, select Check for new release from the Help menu then try again.

Each site is on its own line, the site name first, an equals sign, then a number. The number specifies how Opera identifies itself:

0Default (same as no ua.ini entry). Opera identifies as per your "Identify as" setting.
2Mozilla, Opera detectable
3Internet Explorer, Opera detectable
4Mozilla, Opera hidden
5Internet Explorer, Opera hidden

You should exit Opera before editing this file. Changes made to ua.ini will only take effect after you've exited and restarted Opera.

The file is automatically updated every week from a master copy maintained by Opera Software. The master copy is merged with your own. Any entries you add to your copy that don't conflict with Opera's are preserved. Where there is a conflict, the setting from Opera wins.

User Javascript

Sadly, Opera Software have left some bugs in their ua.ini support. The "Internet Explorer, Opera hidden" setting has mixed in some Netscape characteristics! Thankfully, another new feature in Opera 8, User Javascript, comes to the rescue. On my Opera User Javascript page I have a script that works around this Opera oversight (and adds some extras).

The Proxomitron

Opera have made the decision not to allow user Javascript to work on secure web sites. For those sites, The Proxomitron is still needed. You will need to download and merge my filter file:


Opera has the built-in ability to pretend that it's really another browser. Press F12 for the Quick Preferences. The available browser IDs are at the bottom.

Unfortunately, the fakery provided by Opera is somewhat superficial. There are at least two ways to determine it's still really Opera:

  1. The word "Opera" is always somewhere in the User Agent string.
  2. The Javascript property window.opera exists.

An annoying minority of web sites will use these to prevent Opera users from accessing their pages. Often, there is no reason for them to do so, and Opera would surf such sites without any problems, if only it was let in!

To hide Opera more completely, and hopefully get into such sites, several things must be done:

The ua.ini feature added to Opera 8 solves the first two issues, the last issue can be (mostly) resolved by the user javascript feature added to Opera 8. See my Opera User Javascript page.

Internet Explorer

For the want of putting this anywhere else, here's how to alter the User Agent string sent out by Internet Explorer.

WARNING: This requires editing the registry. Editing the wrong part could totally stuff up your PC! Proceed at your own risk!

Shown below is the User Agent string your browser is sending out. Use it check your changes:

CCBot/2.0 (https://commoncrawl.org/faq/)

So, you want Internet Explorer to identify itself as Opera? Easy:

String NameString Data
CompatibleWindows NT 5.0

Remove any String values in the "Pre Platform" and "Post Platform" keys.

That results in "Opera/8.0 (Windows NT 5.0; U; en)", which is identical to the real thing.