VirusTotal

I’ve been using this free service left and right and it has saved me quite a few times.

www.virustotal.com lets you upload your files and get a virus report. The system automatically tests your file against 40 different virus/malware programs that are constantly updated. Depending on the file size, it could take 10 seconds to a couple of minutes. Many times, you’ll see that someone already scanned that file, and you are able to get instant results.

Don’t open a file you don’t fully trust, send it to VirusTotal first. I’ve had some false negatives with my active anti-virus that were caught by VirusTotal.