Quick response...your ISP is not up to the task... Just because "we" have the fastest hot rod on the block at our end, does not presuppose everyone else in the chain of command does... Your ISP is just a conduit between you and wherever... It gets, and transports whatever is sent to and through it. The files you download may go through any number of hubs, in between, where the service may grind to a near halt... Software that "pretends" to increase these speeds, may do so in micro-seconds only... Is it worth the bother then?
I used to be on a telephone internet service... the ISP limited my uploades and downloads to a given size, especially re: e-mail... Now on cable...but some loads are agonizingly slow, even on it... And, yes, sometimes corrupted by virtue of the transport from A to B... I believe the corruption is a function of the check sum not adding up... you may have the whole file, but if the last wee bit of checking does not jive with the setup files instructions, you are dead in the water until it is corrected.
Try downloading at different times of the day.
Try downloading the same file from different sources.
It does not sound like anything connected to malware...I don't think...
Hopefully, others can add more toward a solution...I am more software oriented then hardware...
Go to the hardware forum for a quicker response, maybe