Now even the brilliantly successful Apple Mac computer has been targeted by an effective Trojan.
This particular malware is Mus Minim, a.k.a. "Black Hole Rat", apparently adapted from the "Dark Comet" Windows Trojan. It includes the generation of "Administrator Password" pop-ups to trap unwary users into entering their username and password, and could appear in the guise of software or games downloads.
Note that a Trojan is not the same as a virus, which replicates by self-installing. Mac OSX cannot "catch" a virus as no software can self-install - a human has to click "OK" as a minimum. Ubuntu is even safer, as there is no user with implicit admin/administrator/root (the terms are interchangeable) rights.
Whichever computer operating system you use, a good tip is always to use a user account with no administrator privileges for normal day-to-day operation. Create a special account with administrator privileges for those times when you absolutely need it.
I'm a regular reader of the excellent SatCure Satellite Review, wittily written by Martin Pickering and full of information about TV reception information. He uses a Mac, and includes a short discourse on Mac Trojans in the latest issue at http://www.satcure.info/reviews/review153.htm .
(Incidentally, if you're looking for more information and/or equipment for digital television, satellite or terrestrial, Freesat or Freeview, then there's no better starting place than http://satcure.co.uk ).
Viruses, and those that write them, are a 21st century plague. They are made possible by the extremely lax programming that underlies the target operating systems. They can install themselves on previously uninfected computers because of an inherent lack of safeguards on those computers. A vast industry has grown up to supply defensive software which essentially covers up the deficiencies of the operating system.
Trojans cannot install themselves without the assistance of a human. The reason they are successful is due to their trickery, making us humans think they are something they are not, like the original Trojan Horse.
Just don't click "OK", OK?