wha is a bug finder?????????????????????????

A bug finder is a program that find bugs in certain programs or in your system
When they say Mac OS X is easy pickings for bug finders is say that Mac is easy to get infect by bugs since they claim to have the "best security" which is not true for now a day.
And in terms of answering your question
Here's a simple way to say it
It is a program that track, locate and delete bugs when the program or data is infected with bugs.

find security flaws in your system

When you're a "bug-finder", you can wear a "white hat" or a "black hat".

If you're wearing a white hat and want to help Apple, you can report feedback at the following URL:
http://www.apple.com/feedback/macosx.html

If you pay $500+ US Dollars per year, you can be a Select Apple Developer and report bugs at "bugreporter" and be taken more seriously than users.
http://developer.apple.com/BugReporter/

Both Apple and Microsoft let you download security updates to the OS periodically to try to stop the "bad guys" from exploiting bugs or security oversights in the OS.

"Bug Finders" find weaknesses in operating systems and software.

Using my elementary school logic, I suppose they find bugs. Or they find covert listening devices.

It simply means macs ARE easily capable of being infected but those who write malware arent interested in the measly 5 percent of the Apple users out there. They are out to infect the masses. I.E., Apple misleads the people by stating apple security is the best when actually its no better than anyone elses computer simply because no one wastes time programming malware for it.