What are User Agents?

User Agent is a client program that was used to access servers on a network, usually the Internet. The HTTP User Agent's header contains all the required information about compatibility, web browser, and the name of the platform used like Windows, Linux or Mac or etc.

The User Agent values property change dynamically depending on the user'sbrowser and platform versions. As example, Microsoft Internet Explorer 6 will returns the following identification under Microsoft Windows XP.

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

The User Agent identification is one of the aspects which crawlers could be excluded from specific pages or parts of any website using the 'robot.txt' file. This will allows any web admin who feel that certain parts of their website should not be included in the data gathered by a particular crawler, or that a particular crawler is using up too much bandwidth, to request that crawler not to visit those pages.

You can check your User Agent for your PC at: http://showip.net/check_user_agent.php

Here's how you can change your User Agents in different browsers:

1. Step to Change FireFox's User Agent

The very first things is to start Mozilla FireFox and type in the address bar url:"about:config" (without quotes).
Next, you right click in the page, Choose "New" then click "String". Now Set name:"general.useragent.override" (without quotes) and now set the value which you want FireFox web browser to use. The next step is: type in the address bar "about:" (without quotes) and try to look at the 4(four)last point. It's now your new User Agent.

Useful information for you:
Most of website admin use some other tricky techniques as example they use on their site a simple technique to get feed Google's spider also known as Googlebot by optimizing web pages in order to obtain a better & higher position as possible in search engines placement. For that, you can change you web browser's User Agent to "Googlebot/2.1 (+http://www.googlebot.com/bot.html)"

For Mozilla Firefox users there is a add-on/plugins called 'User Agent Switcher', of you want to give it a try, then feel free to download it from: https://addons.mozilla.org/en-US/firefox/addon/59

2. Step to Change Opera's User Agent

Opera web browser identifies itself as a version from Microsoft IE(Internet Explorer) by default setting. For Opera version 6, they pretend itself as IE(Internet Explorer) 5.0, Opera 7 as IE(Internet Explorer) 5.5 and IE(Internet Explorer) 6.0. Here's how to change the settings in Opera version 7, just straight away to the Network panel from the Opera's Preferences dialog box and make some adjustment to the value selected in the Browser Id list.

3. Step to Change IE (Internet Explorer) User Agent

Here's how to do it in IE(Internet Explorer)

Go to(from desktop)
Start->Run->regedit
and find the key like this:
HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurr entVersionInternet Settings5.0User Agent
Now you must create 3 new strings/id by using the names "Compatible", "Version" and "Platform" and now it's up to you to set them to the value you want.
As example: If your web browser's User Agent is
Mozilla/4.0 (compatible; MSIE 5.0; Windows NT 5.1; SV1; SomeWebsiteABC; .COM CLR 2.0.50727)
compatible is "Compatible"
MSIE 5.0 is "Version"
Windows NT 5.1 is "Platform"

So, in the end hope this tips will help most of you out there.
Just give it a try.