>Are linux viruses as dangerous as MSwindows viruses ?
Generally speaking, if your file premissions are properly set, a virus can be contained to a user account.
>why do articles writers talk so much about viruses for Linux, if they are not so dangerous ?
I don't know about you, but I consider any virus, worm ect. dangerous. Sensationalism is currently very much in vogue in the media, they think it's the only way to "sell copy".
>I also read that there are things much more dangerous for Linux security than viruses (passwords kits etc.)
Rootkits... These are indeed very nasty! If you ever needed a reason to keep your system updated, and well hardened this is it! Running a small program called chkrootkit should br done regularly.