A computer random access memory is divided into first and second partitions. Each partition has its own operating system (OS). The first partition has a conventional OS and is designated for non-Internet use. The second partition is designated for secure Internet access, and has an OS specific for Internet usage. Software in the second partition cannot write or copy files in the second partition. The size of the second partition is fixed and unchangeable while said second partition is open. Each software application in the second partition is allocated a memory region that cannot be changed, thereby preventing memory overflow attacks. A secure memory is designated for temporary storage of software used in the second partition. Cyclic redundancy check (CRC) values are calculated for all files in the secure memory. To detect unauthorized file changes, CRC values are calculated for all files used in the second partition, and checked against values stored in the secure memory. The second partition can write only to a secure memory using a security arrangement such as password protection or a download memory separate from the first partition to allow files stored in the download memory to be examined by scanning and testing from the first partition prior to being stored elsewhere in the computer.