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UNIX was started in the late 60's but mostly written in the 1970's at a time when the almighty 'Internet' was imaginable. UNIX and especialy the "BSD UNIX" on which OS X is based pre-dates Windows by at least a decade.
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This really depends on what you mean by
started. Unix is a product of the 1970's. Bell Labs and Honeywell worked on an OS based on Honeywell's Multics, which goes back to the 1960's. After Honeywell dropped out, Bell Labs continued the work on a cutdown version of Multics which it called
UNIX. Although the C programming language followed Unix, it helped to get the OS out of the laboratory. One a personal note, I was working as a student intern at Bell Labs in 1974 when K & R's
Programming in C was released as a technical report to Lab personnel.
As for viruses, the spread of viruses certainly speeded with the advent of electronic bulletinboards and the Internet. However, MS-DOS suffered mightily under the burden of viruses transmitted by floppy disk. Although Macs were much more likely to be networked than MS-DOS computers, Macs had fewer viruses. With the advent of viral threats, the Mac community responded with freeware and commercial antivirus software such as the freeware
Disinfectant and Symantec's
Symantec Antivirus for the Macintosh aka
SAM. The design of the Macintosh allowed antivirus software to work with certainty. By the time MacOS X was released, the number of new Mac-specific viruses dwindled to the point where there were fewer than one per year. MacOS X reduced that number all the way to zero (0).
Although networkability enabled DOS/Windows viruses to spread at an increasingly rapid rate, it actually helped to kill MacOS 9 viruses. This was because all antivirus software updates were distributed over the various commerical and free networks and bulletinboards. Also, MacOS X eliminated viruses as a threat to Mac users once and for all. OTOH, Windows XP has seen the most egregious malware ever on the Wintel platform.
"Security through Obsurity" is not a myth. It is an outright lie created by Bill Gates in the 1999-2000 timeframe in response to the heavy onslaught of Windows malware at the time. The popular media, Windows apologists, and the easily convinced glommed onto Gate's lie and accepted it as gospel.