You have just to be careful on what attachments to open...
e.g. no .src / .bat / .exe / ... and .doc / .xls could contain visual basic code...
Furthermore I would recommend you to always display the file extension:
1.) Open Explorer
2.) Click on "View" and then select "Folder Options"
3.) Select the "View" tab. The one between "General" and "File Types"
4.) Disable the option "Hide file extension for known file types."
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