Try sites like this
Fuduntu | Free software downloads at SourceForge.net
There are some details on changing the BIOS I skipped over in my previous posts. Earlier laptops only required a change in boot order ie make the BIOS check USB first, for Linux as an example, and if no Linux found then go to hard drive for Windows.
More modern laptops have an additional complexity. My understanding from web reading is that when Win8 came out Microsoft had computer manufacturers set BIOS up to only allow other versions of Windows to be read from USB - as a way of protecting the system...wink, wink. Alternatives to Windows would not be allowed to run. There was an international uproar forcing the inclusion of some other BIOS settings to get around the 'protection' of resident Windows systems. The extra steps required may vary from manufacturer to manufacturer. Mine is a HP laptop and required from memory two other BIOS changes.
Although I do not understand the processes by which it can happen, it is possible for 'viruses' to lodge in BIOS, but I believe there is also an option to make BIOS read only once you have made your mind up about changes (you can make it write again, if you want to make other changes).
There are other ways of making dual boot systems through disk partitioning, but later versions of Windows, as I understand it, are resistant to changes. XP was I think the best of the last in regard to flexibility - but its been a long time since I tinkered with partitioning for dual boot.
Try reading up on viruses for Windows and Linux (Mac)!
