More and more virusses are created nowadays. But luckily there are also quite clever antivirus software solutions. Sometimes you receive files which you do not trust, but you can't directly see if it contains a virus or not. I came across the VirusTotal webpage which offers checking files on virusses and malware. It maintains relations with many antivirus software production teams, so the more files are scanned (actually the more virusses are found), the better these antivirus programs get in recognizing threats. So next time you encounter a suspicious file: first put it though VirusTotal!
The link is http://www.virustotal.com