This hack report is actually misleading/false, it's been debunked on several sites (including MacWorld, incidentally, a ZDNet publication):
http://www.vnunet.com/vnunet/news/2151455/false-hacking-report-prompts
http://www.macworld.com/news/2006/03/07/hacked/index.php
A second contest was held, where the mac was exposed to thousands of experienced attackers over the internet, and held up perfectly (with the exception of it being momentarily unavailable due to a massive Denial of Service attack, which can happen to any server
http://software.silicon.com/os/0,39024651,39157042,00.htm
Bear in mind that ZDNet often prints inaccurate, distorted stories to bring in hits from angry readers. Their main priority is advertising, so hits are all that matter in that game. Occasionally they get themselves under scrutiny and they have to retract their claims, as we've seen here.
Oh yeah, and all of the "200 Mac Viruses" run in Mac OS 9 and earlier. They can't infect a Mac OS X machine, as they are completely different operating systems from the ground up. The claim of "200 viruses" helps to sell antivirus software for the Mac - which has been shown to actually create more security problems than it solves. You're safer on a Mac, in other words, WITHOUT anti-virus software.
I'm not saying the Mac is unhackable, but the scope of the hacks will be limited to social engineering / trojan horse attacks (requiring the user to manually install a virus in the guise of an application, and enter their administrative password) rather than actual self-replicating worms like we see in the Windows universe. I will start playing guitar for Barry Manilow the day that somebody writes a Mac worm.