RMLLauncher is injecting code (mods) in a running process (the game), and this is a very suspicious action. As a mod launcher we need to do this, but it's not a "normal behavior" for a software. Then your antivirus is flagging it as a Trojan or a malware that try to hide himself in others applications. If you are worried and not sure if you want to download it because of that, you can go on the RaftModding discord server or on the official raft server to ask on the modding area what others user thinks of RML.
Ctrl+R then type
When you are on the Windows Security Center open the Security tab.
If you are on an old windows 10 version, you will have the name of your antivirus here (it's the "virus protection" row).
Else, if you are on the newer windows 10 version, you will have "View in Windows Security" in the "virus protection" row, click on it and on this new window you should have your antivirus name.
Now you will have to have 2 exclusions in your antivirus to avoid all the false positive for the launcher.
The two files are those ones :
C:\Users\Your user name\AppData\Roaming\RaftModLoader
To add the exceptions in Windows Defender you can follow the next link : https://support.microsoft.com/en-us/help/4028485/windows-10-add-an-exclusion-to-windows-security
To add the exceptions in Avast you can follow the next link : https://support.avast.com/en-ww/article/168/
To add the exceptions in BitDefender you can follow the next link : https://www.bitdefender.com/consumer/support/answer/13427/
Check out this help article by Norton to add the files listed above to the exceptions list: https://support.norton.com/sp/en/us/home/current/solutions/v3672136
If Raft Mod Loader can't connect to the internet, you'll need to add an exception to your firewall too:
Open My Norton
Go to Settings -> Firewall -> Application Control
Use the search function to find
Allow network access for
Thanks to Sly for providing instructions for Norton!
Type on google "How to add an exclusion in " and the name of your antivirus after, then go on the website of your antivirus and follow the step for the two files above
If after that you have another error or you still get the same error, go in the #support channel of the Raft Modding discord server and we will be glad to help you🙂