Upon further reading this appears to be a false positive.
Disable your anti virus for this and only this download, Do Not go anywhere else.
Go to this site and dowload the latest patches( I think it is v54 & 55) from here http://maplecrusade.com/
Put them in the Nexon MS folder.
Going into the AV program,find the exceptions
Click the exceptions button (or what ever it takes to enter)
Designate Nexon Folder as an exception.
Click OK or apply to accept the folder as Excused from the scanning process.
Re-enable the AV program.