Well here's the case. There's probably over 200 people using RME, and no one of them has ever complained about getting hacked or something. Which means that the map editor is most likely virus-free and the thing that pops up is nothing but a false positive.
If the file that you scanned gives off the same virus warning as a new fresh copy of RME, downloaded from the official RME website, then that means that they are identical in terms of possible viruses, and since we previously made it clear that said "virus" is just a false warning, both of the downloaded files that you got, both the one from your friend, and the one from the official RME website, is safe.
However keep in mind that even if those virusscan websites gives you an "OK", it does not always mean that they are safe, so I would still suggest using the latest version from RME's website.