I just went on the WC4 page on Gog.com to try and download it again, and the download llink has dissappeared? Have the Gog..com admins finally cottoned on that rhe install is corrupt/virused and took it down?

The install is not corrupted or virused. Are you trolling or do you just have a bad attitude?

Anyway now to answer your question. After purchasing a game, the download links are kept on your "My Games" page.

1. Move your cursor over the "My Account" tab.
2.. Select "My Games"
3. You will now be at a page that looks like a shelf with games.
4. Click on the WC4 box and installing that game and any extras you wish.

I clicked the link to my games shelf, WC3 and 4, no download links. And no, I am not trolling, I have had issues downloading WC3 and 4 for several weeks after purchasing both games, I finally managed to download WC3 last week using Firefox browser.

I just checked and my links are there, so you may have to contact official gog support.

I only have one more possible fix. After you click on the game, make sure "GOG.com Downloader mode" is switched to off.