Virus

If you own an Apple Macintosh computer, should you worry about viruses, worms, and Trojan horses? Yes, but not to the same extent as on a PC. Viruses have been written for Apple computers, but they haven't proliferated to epidemic proportions in the same way they have on Windows-based PCs.

So why not? Well, for one, Apple has designed its operating systems really well, especially the latest one called Mac OS X.

Before the operating system came along, there were about 6080 Mac viruses in the wild that threatened Mac computers. Since, there's been none that have been able to assault Macs running OS X. Apple has had to fix security holes in the operating system and issue patches, however.

Computer viruses are written by a variety of perpetrators. Historically they have been brilliant teenage kids or desperate people in search of attention. They are typically male and in their teens or early 20s. However, David L. Smith, author of the famous Melissa virus, was 30 when the FBI caught up with him.

Still, I like how Jack Sebbag, a vice president at the antivirus software company McAfee, characterizes virus writers: "They're 14-year-old kids who can't get a date, but have incredible talent and are looking for a challenge to bring (millions of) computers down just to get a little notoriety."

JPEG or JPG (Joint Photographic Experts Group) is a popular image format used in World Wide Web. However there is almost no possibility that some virus would be added to this image files since the JPEG didn’t contain an executable code that could be triggered a virus. Some of mechanism of JPEG virus like is just a link or trigger to the infected executable files.

Some more detail explanation for JPEG virus:

• It's not a virus. The posted JPEG is actually a trojan downloader. It has no ability to spread on its own.
• It only affects users
  

A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. However, the term "virus" is commonly used, albeit erroneously, to refer to many different types of malware programs. The original virus may modify the copies, or the copies may modify themselves, as occurs in a metamorphic virus. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD, or USB drive. Additionally, viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with computer worms and Trojan horses. A worm can spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a file that appears harmless until executed.