To return to the OPs question:

Hi rahotra , and welcome to AO.

What is happening is that your ISP has a "blacklist" and will block access to sites on that list. This is sometimes done at government level, and is very common in businesses and educational establishments.

The problem is that these blacklists are frequently imported and are rarely scrutinised objectively. Even AO has been on some of them

Another method is to use keywords for site and content filtering. This has it's own problems in that:

"How to hack your girlfriend's hotmail" would probably be treated equally with:

"How to protect your business from hackers"

Assuming that the material you want is legal in your country you might get someone from outside to download and e-mail it to you.

In educational and corporate environments I have seen central repositories for information. If you could justify it, material would be downloaded for you by someone without the restrictions.

Similarly you could ask for specific sites to be authorised, if they were obvious "false positives"

Cheers