Have you received any suspicious file, attachment you are unable to recognize via email? Best online security practices describe that do not open and run any attachment from unreliable source and make sure you know the sender is trusted. Normally popular services will mark that file as suspicious and put that email in junk folder. You might still want to know about that file before running it on your PC. Here is an online service which will analyze and detect any threat in files and give you details about any file from multiple antivirus engines.