How to get 100% secure debian system?

Hello. I'm a Windows 10 user. Unfortunately, I've used a lot of cracked
programs in the past. I want to switch to debian and use only legal
software. I want to write debian netinst to a flash drive. Is it possible
that the distribution on the flash drive will be hacked through a Trojan or
the sources of downloaded files from the server will be changed during
installation? I create websites. It is important for me to know that my
system is 100% secure and information is not shared with third parties.