Should I be leery of opening email attachments?

I & a friend exchange emails fairly often, & recently she sent me some emails that had attachments. I’m deathly afraid of getting a virus through an attachment, so I saved them to a disc. I worked up my courage & decided to open them, but none of the programs on my computer would do it because the files ended with .dat. I then had the option of looking on the web for software that would open them, you know the rest, yadayadayada.
If I had just opened the attachments without saving them to disc, would they have opened without this .dat business?
Am I being paranoid about viruses?
Is there anything else I should know about attachments?
Thanks in advance to any & all who may reply to my questions.

I’d never open an attachment in an email from someone I don’t know. That’s not to say a friend wouldn’t unwittingly send you some bad news attachment, but at least you’ll have somebody to yell at in that case.

The *.dat files are most likely ascii files that you can open with Notepad or Excel.

What you don’t want to open are *.exe files.

It’s good common sense not to open attachments you’re uncertain of, so you’re not being paranoid. Even if you recognise the person who sent the email, it’s possible that they have a virus that sends out its own mail to people in their address book without the user knowing.

Generally, and in my experience, the most suspicious attachments are image files (which have filenames often used to disguise VBS viruses) and executable programs (.exe files). I generally delete these emails without even thinking of opening the attachments, even if I know who sent them. Even the best anti-virus software is usually only as good as its last update, so a new virus may not be stopped even if you only updated yesterday.

.dat files could be many things. It could be a virus, or it could be genuine. I’ve seen the .dat suffix used by different programs to indicate a data file. It could be a text file (in which case Word, WordPad or NotePad would open it fine) or it could be a program-specific data file, in which case it’s useless without knowing what program is needed to open it. I think it’s probably to steer clear and get some confirmation from your friend just to be sure; it would be an unusual file format to send out assuming you could open it.

According to, a .dat file is almost any kind of data file:

Id be suspicious of a .dat file sent all by itself.

In general, be suspicious of attachments that you were not expecting, or attachments that the text of the email does not explain. The sender should say something to the effect “Here’s that spread sheet you wanted”, or “Listen to this clip of my boss on the toilet!”. If the text of the message makes no mention of an attachment, don’t open it until you can verify the sender really meant to send it.

Optionally, get youself a Hotmail account and forward it there. Hotmail claims to scan all all attachments with McAfee, while offering the standard disclaimer.

The best advice on opening attachments that I’ve ever heard is:

Never open anything from anyone who isn’t close enough to strangle…


I second the advice about not opening an attachment if you’re unsure of it. It’s a cost/benefit thing - are you really willing to pay the price potentially of losing your computer, and having to rebuild it, for the joy of seeing dancing hamsters on your screen?

As an aside - if the “.dat” files are named “winmail.dat”, they may be just an innocent attachment that Microsoft Outlook adds to outgoing e-mails.

I have a question along these lines. Assuming I don’t use a souped-up mail program like Outlook, and assuming I’m shrewd enough to figure out file extensions, has there ever been a case of a virus being transported by any file type other than an executable? Normally I feel pretty safe about opening .jpg’s and stuff without worrying about where they come from. The worst that could happen is my briefly laying eyes on an unsavory picture, right?

Also in my experience, if it’s someone you know, you can almost always tell that the letter involved is virus-generated. If it’s as vague as, “Hello! Here is that file you asked for! Enjoy!” then I realize what I’m dealing with.

Archenar – good advice; the vague message is a giveaway.

And you can only get a virus from an attachment that’s executable – .gif, .jpg, .txt, etc. are safe if that’s what they really are. Some viruses, though give a double extension (i.e., file.txt.vbs). If you’re not displaying all extensions (you should, but the Windows default is to hide them), you can get caught.

If you get an attachment from a friend, especially one with a vague message, send an e-mail back asking what it was (though this isn’t infallable – one virus a few years ago sent an automatic reply that the message was clean. Changing the subject line would avoid that one).

There’s the Word macro viruses that hang out in the DOC files. Not all executable files end in EXE; other files that could potentially contain executable code include ones that end in VBS, COM, SCR, PIF, and the now almost never seen BAT. It may be possible to infect DLL files too. It’s concievable that someone might right a virus that infects uncompliled programs, which typically have extensions of C, CPP, BAS, and quite a few others, but that would not be likely to get very far. Some files may masquerade as JPEG’s, but if you look closely (and don’t tell your computer to hide file extensions), they actually take a name like “me_naked.jpg.vbs” or something else where the executable extension has been tacked on.

Viral code does no good unless it is in a place where the computer can consider it to be a set of instructions. If I typed out the code of the old STONED virus and posted it to this message board, while it could set off an anti-virus alarm, it couldn’t infect your computer. As far as the computer is concerned, the data in a non-executable file is not an instruction for the computer. There is a rumor that one Microsoft MP3 player would execute virus code, but this was simply because the program was very badly written.

Perhaps you and your friend should agree beforehand to take all attachments you wish send to each other and zip them before sending.

If you’re still nervous about it, try this:

A: "Hey, I have a Word document I’m about to send you. It’s called aboutme.doc. I’ve already scanned it for viruses, etc., with my Norton’s/McAfee/Trend. It’s in a zip file that 25,678 bytes in size and password protected. The password is ‘openme’ (without the single quotes).

B: “Got it. The zip arrived fine. And I scanned it, too, and found nothing. One problem, though.”

A: “Whut?”

B: “Your Word document aboutme.doc was blank …”

Flowers, I was re-reading your post and i see you mentioned that you were afraid of getting viruses through attachments so you saved them to disk and opened them later. Saving them to disk does nothing to discourage the virus, you’re just moving the file’s location. Not sure if you knew this so I just figured I’d chime in.

The best thing for you to do, as people have already said, is just ask your friend if they intended to send you an attachment and ask what it is. If they didn’t, you could be helping them out by letting them know they might have a virus and may be sending malicious email without knowing it. If you have a bunch of these things that your friend din’t mean to send, you can take extra precautions by deleting the files from wherever attachments are saved. You can also most likely find an option in your email program that lets it know to delete attachments when the email itself is deleted. I know some programs don’t do this by default.

Is it possible there are people who still don’t run a comprehesive virus scanning program like Norton or Mcafee? I use Mcafee VirusScan Online, which gets automatic updates 2-3 times a week, and it has caught dozens of infected emails (some, such as Klez, I get several times a week!). Why worry about what to open or not, just get a good scanner and reduce the stress in your life!

Just a quick tid bit to add. Reading a file with notepad (that comes wit windows) or another basic text editor (that don’t run batch files) is safe. So if it was a text file you’d know, and if it wasn’t, you wouldn’t be any worse off.


Well. Fear Itself, I’m glad to hear that you have the funds and the freedom to PAY for virus updates. They’re not free, you know, and many people either don’t have the money to pay, or don’t have the right to buy it for their work machines (and the boss just doesn’t get it).

Me, I have a Mac. No one (well, hardly anyone) bothers to write viruses for the Mac.

Actually, the DOS version of F-Prot is free to individual users, as are the updated sig files.

I’m just an ornithologist, but part of my job includes a little lan admin for a p2p departmental network. A little cajoling/pleading/tantrums and finally threats of cutting off internet access was all it took to get those pesky professors to use an antivirus (and firewall) and to keep them updated daily (as well as daily mandatory scans and updating the OS). I also offer them techniques to decrease the likelihood of infection, including not opening attachments without first scanning them. As a matter of personal practice, I first save attachments (I receive weekly data from 21 counties, plus powerpoint presentations once a year) to a folder and do a manual scan. Yes, it’s already been scanned by my antiviral program, but it’s part of my routine to ensure that I think about what I’m doing. It only takes a few seconds.

Because it’s only partly true. A new virus can hit you faster than a new update - you’re relying on the A/V provider getting the virus, analysing it, updating the A/V signature file and contacting you before someone sends you the virus. A/V software is a big help, but it’s not foolproof.

I do have Norton 2002, & do get automatic updates, but there is always the possibility of a virus still getting through. I just recently had to do a full systems recovery twice because a trojan horse got through somehow, & my computer locked up completely. It was not pretty.
I’ll email my friend & see about doing the zip thing with the password.
Many thanks to all who replied!!!

Couple things that I don’t think were mentioned:

  1. If you receive an email from someone you know with an attachment but are not expecting the attachment, email them back and ask. If, as said earlier, the subject heading makes no sense (“Look, my beautiful girlfriend” or “Eager to see you” are two I received just today), then don’t open the attachment.

The reason I mention this is that even if you know the person, the attachment could be a virus. The Klez worm works by taking the address book on someone’s PC and emailing itself to everyone in that book. If your email address was in that address book, you’ll get that email, and the PC owner would never know.

  1. If you get an email with an attachment and use Microsoft Outlook (which is the email client that gets beat up the most by viruses), then you can actually read the message without opening the email. Select the message and right-click it. Choose Properties, then click on the Details tab. Click Message Source, and you’ll see the entire text of the message. If you just see a zillion characters with no rhyme or reason among them, delete it.

Correct, but a Mac user who does not take the same precautions may very well be a Typhoid Mary, not knowing they are regularly infecting others while they themselves operate a system immune from such problems.

BTW, once your purchase Norton’s or McAfee, for example, the virus updates are free. And if you cannot afford this inexpensive software, you can always download the latest trialware versions with the latest definitions and be relatively safe.