Files are scanned after they are downloaded, but before they are executed. Just downloading a file won't get you infected anyway, you have to execute the code somehow.
quote:
Originally posted by davidpolitis
I was wondering if someone could make a script that checks the name of a file that someone is sending you & uses a website to check if it could possibly be a virus or spyware/adware.
Checking files on filename is a very bad way to check for badware, anybody could simply change a filename. And even if it would be a good method, maintaining a site and keeping it up to date with all the latest threats just takes too much work for normal people.
I suggest to just a normal virus scanner, which not only scans files send on Messenger, but all the files on your PC.