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How do viruses get onto my computer? What can they do?

Viruses are programs written by malicious people. They can get onto your computer in a number of ways. Most commonly, you acquire a file from someone else and open it, typically when you:

  • open an email attachment
  • download and open a file from a web site
  • open a file from a disk you plug into your computer, like a flash drive, external hard drive, etc.

It generally, starts out very simply: you receive and open a file. This causes a program to run on your computer. Once it is running, this program can do anything its author wants to your computer. A virus, at a minimum, will copy itself into one or more hiding places on your computer, and set up your system to run it every time you turn on your computer. Most modern viruses notice when you are on the Internet and, without your knowledge, send copies of themselves to others via email, leaving no trace in your email program.

Viruses have also been known to:

  • Enclose a copy of a random file found on your computer with the email they use to spread themselves, trying to distribute personal information about you; I’ve seen short stories, photography invoices, and private legal memos.
  • Use a fake return address on the email they send, making it almost impossible for someone who receives their infected email to know that it came from you, and also preventing anyone from notifying you that your machine is infected.
  • Rename, move, or delete files from your hard disk.
  • Scan your computer looking for email addresses (not just from your Address Book) to use.
  • Scan your computer looking for your writing, and then using phrases that sound like you to trick others into opening the copies of the virus sent out via email.
  • Slow down or crash your computer; sometimes this isn’t intentional, but due to viruses that were poorly written.
  • Move icons around on your desktop.
  • Try to delete or disable your antivirus software.
  • Wait weeks after first arriving before doing anything, so you won’t associate any particular email you opened with their behavior.

You should also be aware that there are a small number of viruses that can infect your computer when you do things that don’t involve opening a file, such as:

  • opening an email that does not carry an attachment
  • visiting a malicious web site

These viruses usually exploit specific combinations of circumstances (a particular version of email or web browser software), so they’re not very common. Don’t let these potential problems scare you. If you haven’t already, you should get good antivirus software.

If you have additional questions, or if you need some help to buy, install or update your virus protection software, contact me at (617) 484-6657, martin@kadansky.com.

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