I had a problem with corrupted download in Windows 8, it was very frequent and network-driver related, I don't like ESS firewall, its way too buggy but you should check if isn't drivers.
It could be a combination of issues but is not exclusively a driver issue as I have a different security suite on it today to test the issue and it is just fine with another suite. -Disregard that, the problem came back. I think DownloadStudio just does not work well in its current form.