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It's not really true that viruses attach to emails after they leave your computer. One confusing issue is that some email is read on the local computer, and some is accessed online; those two methods have different problems.

I have a question about virus attacks. I was told years ago that most all viruses actually attach to the message packets after it leaves the computer and before the email arrives on the recipient's computer. Is this still pretty much true today? Like a Trojan virus; I've told folks that their computer may not actually be infected but to scan it, as they should already be doing. Am I way off base with this?

In this excerpt from Answercast #30, I look at the idea that viruses attach to emails after they leave a computer and the different problems associated with local and online email accounts.

Attaching viruses

No, you're not way off base.

Virus scanning is always an important thing or an important part of the arsenal we use to keep ourselves safe; but there's definitely a misunderstanding here:

  • To the best of my knowledge, it's never actually been true that viruses attach after your messages leave your computer.

If a virus is going to attach to a message that is coming from your computer, it's going to do so on your computer: when that message is composed and sent.

Online and offline email

What's confusing things here, I think, is the current rash of online account hacks; where people's email accounts are getting hacked into.

  • Their computer isn't involved at all.

Basically, a hacker learns their password or somehow cracks their password, and logs into their online email account from some other computer – somewhere else on the planet. Once they've logged into their email account, they can then start sending mail like crazy including, if they so desire, attachments that happen to be viruses.

That looks like it's mail that came from you, but it didn't; it came from the hacker; it came from the hacker's computer. It came from the hacker accessing your account online – rather than actually doing anything nefarious to your computer.

Virus attaching to email

So, both are possible. But, like I said, if a virus is going to attach to an email that you send from your computer, it's going to attach:

  • When you send it;

  • Or it's going to start sending email from your computer with the virus attached.

That's in the decline right now. It's not as common as accounts being hacked online, and hackers logging into accounts directly and then sending email that way.

Article C5520 - June 27, 2012 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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