1. A method for preventing hacker attacks and virus infection in a computer system comprising: when performing a boot procedure for an operating system of said computer system, allowing temporarily writing to a write-protectable area of addressable system memory, said write-protectable area of system memory comprising at least one limited range of addresses of said system memory and being fewer than all the addresses in said system memory, wherein said write-protectable area of addressable system memory is write-protected by a physical write-protection mechanism comprising a physical write-enable/disable signal line transmitting a signal voltage to said write-protectable area of system memory, said signal voltage being selectable by a switching means which is exclusively operable from outside of said operating system of said computer system; storing a first portion of said operating system containing security-relevant information into said write-protectable area of system memory; prompting a user to perform a manual switching to restrict writing to said write-protectable area of system memory, thus resulting in generating a write-protected area of system memory; restricting any write access to said write protected area of system memory in response to said manual switching during further runtime of said computer system; storing a second portion of said operating system different from said first portion in an area of said system memory which is not write-protectable to complete said boot procedure; and after said restricting any write access to said write-protected area of system memory and said storing a second portion of said operating system different from said first portion, reading data in said first and second portions and writing data to said second portion to operate said operating system during runtime of said computer system.