HOW TO SEE IS THAT A VIRUS ATTACHMENT?

To identification of virus attachment:
a). it has a small size ( <150KB )
b). it has extension file name such as below:
*.scr
*.clp
*.pif
*.bat
*.exe
*.com
*.txt
*.doc
*.lhz
*.rhz
and some time it's compressed by *.zip file.
Also by the fake name HotMovie.MPEG_ _________ scr.
Actualy the file is virus file with extension .scr