Linux was created in the early 1990s based on the Unix design of the 1960s.
First part of this myth is that hackers want access to home users computers not the large Unix servers.
The point of hacking was (and still is) to gain access to the high end computers. Most of them ran Unix or Unix based operating systems.
Trojens and viruses are the ultimat means of hacking into any given computer. If it was truely as easy to make a Unix virus as it is to make a PC virus then every hacker would have at least two Unix viruses in his or her toolkit long before the creation of Dos.
The second part of the myth is that Linux hasn't been around "long enough".
It was only a handful of months after Dos receaved the ability to multitask in the background. At this point in time the vast majority of home users still had Commodore 64s, Apple IIs and other 6502 or 8080 based computers.
IBM PCs were still primaraly small to medium sized business machines.
The viruses were created for and targeted at BBSes. Only a tiny handful of people were expected to be infected. However the viruses were far more powerful than expected.
Linux was already a decade old and had a larger userbase than Dos did when the first clames of Linux being too young.
Now Linux runs on nearly all the servers (the target of every hacker), Linux is older than Dos was, Linux has a larger userbase than Dos did.
Also there were viruses for the Amiga, Atart ST and other platforms that died due to lack of sales.
Size and age weren't the desiding facters.
The ONLY factor involed in the creation of a virus is the possability.