Computer users are being warned by industry experts to beware of secret codes which could be used to record their conversations.
Emails, screensavers, and electronic greeting cards can carry a secret code which is able to switch on the computer's microphone, make a recording, and forward it to someone else without the user's knowledge.
In fact any attachments sent to a computer, be it a game of Space Invaders, or a moving image, can potentially be used to spy.
Experts say people should always think twice about opening attachments because - although rare - bugging by computer can, and has been done.
Bill Lyons, head of the internet security company Finjan, said: "Military people in the United States have tested this and you can be sure, if people in general are aware of it, then computer hackers are aware of it.
"The frightening thing is, there are tools on the internet which people, using a simple search engine, can find which will enable them to bind this malicious code to simple attachments."
Experts have also confirmed that what can be done with a computer's microphone could also be done with a webcam - allowing pictures to be taken of people near a computer terminal.
Carl Saran, from Computer Weekly magazine, said: "I don't think this is scaremongering - it is potentially possible.
"I'm sure there are clever people who are thinking about how they can use this feature to look at what people are doing on their computers."
Het komt er dus op neer dat het mogelijk is dat er in e-mail attachments codes zitten die je microfoon aan kunnen schakelen, vervolgens opnemen wat je zegt en dat dan weer doorstuurt naar een willekeurig ander e-mail adres. Wat leuk