Filesize: 498.36 MB (522565534 bytes)
ISO MD5: B5DE7A10DD1586D47535372EA1AD9BED
ZIP MD5: 5B8E9240AE8CF74939B60AD872CBBABA
It appears you installed some downloader but here it works fine. I'd research how to get rid of that download manager and just use what the browser offers.
It sounds as if some HIJACKING of the browser has occured. I'd use Grif's advice at link too.