ZIPPED FILES. Emails with attached ZIP Files are potentially dangerous if the ZIP file is password-protected, because the virus-checker cannot scan the contents. The password is generally sent to you in the email-message and it asks you to open it.

By default, Windows suppresses file extensions. This allows virus writers to make use of a double extension ruse to fool users. This is how many of the current viruses are infecting PCs - when people receive an email with an attachment (perhaps from someone they know) and they run the attachment.

 

If you get an attachments that look like this "A JOKE.JPG.EXE" then you know it is a potentially damaging executable and NOT a JPG. Having a fake extension is seriously suspicious.

Beware, the other day I was sent a virus that looked like this

"A JOKE.JPG                                                 .EXE"

... the name was so long that you couldn't see the .EXE part. The icon of the file alerted me because it was not the normal JPG icon.

To double-check you could save attachments to your harddrive (easier to see the full name), and then scan them for viruses (often a right-click on a file gives you the scan option, and this action is safe if it is a virus - just don't run it until you are sure (normally left-double-click runs files but it can sometimes be single click or even right-click if someone has changed the mouse settings so check first!).

If you get an executable and you believe it is a self-stracting ZIP file , then you should right click and use your ZIP softwate (WINZIP. PKZIP, WINRAR etc) to extract the files - never just run the EXE file unless you are certian it is safe.

If you get an attachments that look like this "A JOKE.JPG" and you are certain JPG is its real extension then it is safe to open it (same goes for any raw data format like MPG, BMP,AVI, TXT).

If you get attachments that look like this "A JOKE" then you should change settings so that you can determine the extension of a file

How to make sure you have file extension viewing enabled: OpenWindows Explorer and select Tools | Folder Options. Click the View tab, select "Show all/hiden files" and deselect (uncheck) "Hide file extensions for known file types".

Optional task for advanced users : The above instructions will display all file extensions except for .SHS files. To display .SHS file extensions, one additional step is required. After following the above instructions, users must then edit the Registry, HKEY_CLASSES_ROOT\ShellScrap, deleting the value "NeverShowExt".

Following is a list of the common file types that should be considered suspicious when received in email and should not be opened unless you requested or expected the attachment:

EXE , PIF, SCR, BAT, COM,

Below is a list of most of the filetypes that could possibly do damage,  
although some are far less likely to cause problems than others.

ADE	Microsoft Access Project Extension
ADP	Microsoft Access Project
BAS	Visual Basic Class Module
BAT	Batch File
CHM	Compiled HTML Help File
CMD	Windows NT Command Script
COM	MS-DOS Application
CPL	Control Panel Extension
CRT	Security Certificate
DLL	Dynamic Link Library 
DO*	Word Documents and Templates
EXE	Application
HLP	Windows Help File
HTA	HTML Applications
INF	Setup Information File
INS	Internet Communication Settings
ISP	Internet Communication Settings
JS	JScript File
JSE	JScript Encoded Script File
LNK	Shortcut
MDB	Microsoft Access Application
MDE	Microsoft Access MDE Database
MSC	Microsoft Common Console Document
MSI	Windows Installer Package
MSP	Windows Installer Patch
MST	Visual Test Source File
OCX	ActiveX Objects 
PCD	Photo CD Image
PIF	Shortcut to MS-DOS Program
POT	PowerPoint Templates
PPT	PowerPoint Files
REG	Registration Entries
SCR	Screen Saver
SCT	Windows Script Component
SHB	Document Shortcut File
SHS	Shell Scrap Object
SYS	System Config/Driver 
URL	Internet Shortcut (Uniform Resource Locator)
VB	VBScript File
VBE	VBScript Encoded Script File
VBS	VBScript Script File
WSC	Windows Script Component
WSF	Windows Script File
WSH	Windows Scripting Host Settings File
XL*	Excel Files and Templates