Easy: GNU/Linux system are vastly less vulnerable than Windows systems, for at least 2 reasons. (1) Their users tend to actually know how computers work. Theref

Easy: GNU/Linux system are vastly less vulnerable than Windows systems, for at least 2 reasons. (1) Their users tend to actually know how computers work. Therefore they are far less vulnerable to mind attacks (such as hot_chick.jpg.exe). (2) They are more up to date. This is partly a consequence of 1 (users care about security patches), and of "piracy" (illegitimates copies of Windows tend to not be updated frequently). Also, there are many GNU/Linux distributions out there. So, a security breach on one system may not be there on another. Plus, the virus has to be portable. Anyway, this focus on viruses is probably misleading: GNU/Linux systems are attacked. Regularly. For instance, any new machine with an ssh login will log more than 500 login attempts a day before the end of the first week. Those attacks may just not attempt to install a virus. They do some other "interesting" stuff, though, like adding a web page at www.yoursite.com/secret-loc/gimme-credit-card-number.html, or sending spam.