From hiveworkshop which was from thehelper.
Post describing possibilities.
The exploit allows any malicious map maker (or map hoster) to insert code which downloads a file anywhere on your computer the next time you restart your computer (after loading the malicious WC3 map that is).
Possible usages includes downloading files to your startup folder or overwriting existing popular program files (skype, steam, etc) with maliciously modified versions for example.
Basically don't download or join random or odd WC3 custom maps (host your own games using maps you know are "clean" [maps that you played dozens of times without any problems]).
Fortunately the exploit hasn't been taken that much advantage of yet but I think it's still worth a mention in case you do play random WC3 games a lot and you have things you do not want to have taken over or lose (battle.net account passwords in case a keylogger gets downloaded to some location where it can be run through some program or autostart, etc).
Existing maps people have been playing for ages are probably safe and popular maps are safe too (well known authors of maps would not likely inject malicious code into their maps).
However there could be "clone maps" which have the same name and preview but with the malicious code in the map; those maps are the ones to watch out for (if you see you're DLing a map you already own, you should leave right away).