McAfee Manufactures Virus Threat: Backlash by thoughtful people against the (thoughtless) news I propagated here, that we should be afraid of .jpegs bearing viruses. Little more than fearmongering by the “group of 20 or so companies whose profits are directly linked to creating fear in their customers, who have to keep discovering new sources of fear to improve their bottom line – or in the absence of new discoveries, keep inventing new sources of fear” — the anti-virus companies?

Now, if you know much about computing, you may be a little suspicious of this. JPEGs are compressed image files that only contain data representing an image to be displayed, not code to be executed. A modification of that data might screw up the picture of your cat dangling from the edge of the kitchen table you like so much, but it won’t turn the image into a potential virus transmitter, because the programs that display JPEGs don’t read them with an eye toward executing the code. An image file is just data to be displayed. The line between “data” and “code” is a little bit fuzzy – often particular characters or a particular file can be both data and code, depending on the context of how other code handles it. Or a particular file can include both data and code separately, like a Microsoft Word file that includes data (your text) and code (some macro designed to be executed by Word when the document is opened).

But for JPEGs there’s a well-designed standard, and it doesn’t include executing code of any sort. If a JPEG-handling program doesn’t like the data it sees, it should just stop trying to display the image, not decide to start executing code from the image. JPEGs are mostly harmless. Slashdot