The website of the niger delta avengers was blocked this morning.
404 errors mostly mean any one or more of the following things:
1. The path/URL is incorrect. It happens when you type wrong path inside a website. If the page inside the site you are looking for doesn’t exist then you can get 404 error. If the URL you are requested doesn’t exist, but its host or homepage does, it can show 404 error
2. You don’t have access to it. Some websites are limited within an area or a country. This can give 404 Forbidden error.
3. You are trying to access a file in a site that is forbidden to you. For example trying to access the admin dashboard without being one.
In your case, it seems that the website you are trying to access is down temporarily or permanently. Maybe its down for maintenance.
Meanwhile,their twitter handle is still alive