avi and security check

I render a project in an avi uncompressed mode. I then call up windows media player and try to open the file. As soon as I get to the folder that contains the file a windows security warning pops up and tells me that my computer is in closing the program because my computer may be in danger. Is my anti-virus seeing this as a possible problem or what? Can I change some setting to allow me to open the file? Thanks