Virus Scanning help [php]

[p0w3r0fchr1st]

I am trying to make a file scanner to check if it has viruses with php. I made the upload form already. Can someone help me with the code? I heard you can do it with clamscan. I tried:

exec("clamscan /var/www/upload", $file, $return)

if ($return == 0)
{
echo "clean"
}

else
{
echo "virus!"
}

But it always comes out as infected, even if it is not. Help please? show me the right path or somethnig. Or just the right code.

thanks