I didn't have that problem with it. I did however have problems using the program - but they were similar to the ones I've had before with CS4 and with other software from time to time.
Things like the program crashing on exit. I'm amazed at how many commercial programs have that issue, not just TGC. For me the most annoying problems with the download version were:
1. the fact it couldn't find the Help files (which were there and can be read outside CS4);
2. the fact it couldn't locate most of the textures the second time I ran it (my guess is that something like a config file gets screwed when it fails to close properly);
3. one of the crashes left a stray window open which Task Manager couldn't detect and the only way of getting rid of it was to restart the laptop which then allowed Windows 10 an excuse to, yet again, attempt to install the W10 Creators Update (which it just can't do on this machine and just prevents me doing anything useful for half an hour
). For some odd reason "Restart" has the same effect as "Upgrade and Restart" - and I keep forgetting that.
I think the download is safe - the Virus Checker is probably taking the default action for something that was created for an older version of windows. I find I have to override all sorts of anti-virus warnings for some software. For example, Norton SONAR wanted to delete most of my DBPro exe files at one point on the grounds that "fewer than 5 people use the file". I ended up banning SONAR from checking most of my folders.
Of course there might be a problem with the download ...
But someone who is familiar with CS4 might find it useful.
Edit: There may be a way around the problems. I've just tried uninstalling CS4 and reinstalling it. I then tried again. I successfully made some test maps and objects and then closed the program using the Exit option from the File menu. This closed correctly. (Yippee!). I then opened CS4 a second time and successfully made a new object and then tried closing it using the Windows Close button (the familiar one on the top right of the window). That created all the problems I encountered yesterday. 
So it seems you need to resist the temptation to close it the easy way. 
I suspect there is a simple settings or config file that gets screwed up when you try to use the Windows Close button. I'll do a bit more experimentation to see if I can find out which one - there might then be a simple fall-back option. 
[Of course the present Uninstall/Reinstall option is always there - and doesn't take very long (if you kept a copy of the download file of course ).]
