$ As this question is asked regularly I have made the post a sticky - JS $
Seems like Atmel eradicated AVR Studio 4 from their website entirely, but there is a torrent for AVR Studio 4.18.
Download the .torrent file here:
[EDIT: removed the download link because it actually is available at atmel.com]
Open it with your favorite torrent client to get AvrStudio4Setup.exe.
It worked for me! Please consider downloading it and seeding it for others, even if you dont need it yourself.