Why do I need a specific "user agent" to access some websites.
I have received instances "You need Internet Explored 6.0 or better to access this web site"
Why should I install a "user agent" extension in Chrome. Is there a workaround? If I install the extension will it devoid my browser's security.
Installing any extension can lessen your overall Browser security - so make sure you download from a known and trusted source. Best to use the browser recommended addons and then look at the comments to see the stability and any potential issues.
In terms of the User Agent - this is an old technique used by some websites to change the website page content depending upon the browser being used.
Some websites that have been implemented with specific browsers in mind block access to browsers it doesnt support. Usually the less used browsers are affected and changing the User Agent is a way to fool the website (if its been poorly programmed) to believing it is a supported browser that it is serving its content to.
It will not affect your overall browser security - google chrome is well sandboxed anyway.
You can use an extension to change the User Agent on a per-tab basis. However, since v17, Chrome has this capability built it.
Let me show you...
press CTRL+SHIFT+I to go into developer mode.
Click the Settings symbol as shown.
Expand the pane as shown and click the Override User Agent tick box
Choose the user agent you want to emulate.
Close Developer Mode via CTRL+SHIFT+I
User Agent is an HTTP header (i.e. one of the strings your browser sends to the server) which identifies... well, user agent, i.e. which browser is used to access the page
i.e. when accessing google.com, my browser sends something like this:
Some sites use User-Agent header for "browser sniffing", i.e. to check which browser is used and to provide different code to different browsers. This was more popular ~10 years ago when browsers capabilities varied wildly.
Installing a Chrome extension would allow you to change the string your browser uses to identify itself (btw, Opera has this built in). This may fool some site, but it does not change browser behaviour (i.e. it does not make Chrome to render pages as IE not does it add support for, say ActiveX components - which, in fact, may be the reason why that site requires IE6)
So, provided the extension you're going to install is safe itself, the level of browser security will stay just the same.
(as a web developer I have serious doubts that any web site which works in IE6 only is worth visiting...)
I don't have a working chrome at the moment to test anything, but you can set the user agent via
chromium-browser --user-agent="Firefox/3.5.5