The file may be considered suspicious by some anti-virus softwares because it is UPX packed. Generally, anything that is UPX-packed will be labled as suspicious. You can download the UPX command-line tool and run "upx -d micromacro.exe" to unpack it, then scan it again. You'll see it's safe.
And, as others have said, everything is open-source. If there was anything that could be used to steal your account, someone would have noticed it by now. In fact, I've went out of my way to prevent MicroMacro from being used to steal passwords and such.