If you want to do a scan independent of your locally installed anti-virus client on a particular file that you have either downloaded (and hopefully not opened yet) or received in an email attachment (and hopefully not opened yet), you can use an online virus scanner to inspect the file to see if it detects anything malicious. Can certain malware infected files evade detection from your locally installed anti-virus client and an online scanner(s)? Of course, but doing some simple checks can lower your risks of getting a bugger that will look to inflict some damage on you and your device.
Here is a list of online file scanners you can use to inspect a particular file:
Online File Scanners:
Jotti – file size limit of 25 Megabyte. Uses multiple scan engines.
Metascan online – Supports files up to 80 Megabytes in size, scans with 40 different engines.
VirScan – Free service that accepts files up to 20 Megabyte in size and scans them against multiple antivirus engines.
Virus Scan – file size limit of 25 Megabyte.
Virus Total – email upload option, 64 Megabyte file size limit, can scan web pages.