As long as you have the oldest versions circulating to your account name, no one can steal it.
Infact, it is advisable to keep the map open source so people can edit it as one day it may need fixing (like with 1.24 patch) and if you are not playing then, the map will be lost forever while if it is not protected, someone can always fix it for you.
All ownership disputes occur if 2 people release the same map at the same time or if the orignal author never has concrete evidence as to why it is his.
I advise to all map makers to submit an optimized version of finished maps to the maps download section (not optimized and not just protected) while also providing in the comments a link to the unproected version or an older unprotected version (any save systems have to be removed and for popular maps it may be best to not have the newest unprotected avalaible to everyone). This way people can not steal it from you (as you will always be the oldest reference to the map existing) while still allowing them to learn from your map or have fun with it.
On battlenet, remember that you can always host or get bots to host your version, no mater how many fakes that are made.
Still this is my advice, if everyone did this WC3 would have like 100s more good maps but it is not up to me to make people do it, purly point out the idea.
