The SDL Tridion World website has been moved and all content is migrated. If you try to access the domain http://sdltridionworld.com you will be redirected here (the Tridion Developers group on the SDL community website), and in case of a deep link, you will be redirected to the location where the specific content has moved. Below is a short overview of where the most important content has moved to:

• Articles - https://community.sdl.com/solutions/content-management/tridion/tridion-developer/b/weblog
• eXtensions - https://appstore.sdl.com/web-content-management/
• Release news - https://community.sdl.com/solutions/content-management/tridion/b/product-announcements
• Trainings - http://www.sdl.com/trainings/sdl-web.html 
• Certification - http://www.sdl.com/trainings/certification.html 
• Support - http://www.sdl.com/support/
• Hotfixes - Contact Customer Support or use your CS FTP server credentials, see also https://gateway.sdl.com/apex/communityknowledge?articleName=000004857