I'm not seeing a _new_mimetex there, just a mimetex Rev=1.1, Age=23months. Are you looking at something else?
Anyway, 23 months is kind of old. You can download a current FreeBSD/Intel pre-compiled binary image from
Unzip that mimetex.zip file, and the included mimetex.cgi is your FreeBSD/Intel binary image. Does that give you an antivirus warning, too?
By the way, the same instructions apply for Windows and Linux/Intel pre-compiled binary images, too, except download
respectively. (Note: the pre-compiled binary image in windows/mimetex.zip is called mimetex.exe rather than mimetex.cgi)