Windows 10 version 1603 doesn't exist — the versions are 1507, 1511, 1607, 1703, etc. If you need 1607 (Anniversary Update) for legacy hardware/software, Microsoft no longer hosts it publicly, but:
Instead, here’s a to get an older official Windows 10 ISO (like 1607 or 1703) safely: windows 10 1603 iso download repack
By doing it yourself, you get the size savings and tweaks without the malware. Windows 10 version 1603 doesn't exist — the
: The third major stable build, which serves as the basis for the Long-Term Servicing Branch (LTSB) 2016 . Safe Downloading Microsoft no longer hosts it publicly