Investigated, reproduced and provided corrections for various system security problems. Specifically customers reported various denial of service (DOS) problems such as flooding daemons with bad data, improper access to system services or files, or simply causing the system to hang or crash. The latter is the simplest form of denial of service. The system is deliberately paniced and therefore is unable to perform its routine operations. NFS is particularly vulnerable to DOS attack since it is inherently intended to be used in a trusted environment. Many systems level programs and services are vulnerable to "buffer overflow" attacks. A buffer overflow occurs when a malicious user sends data to a program or service which overflows the variables or stack that is intended to contain the data. Once the variable or stack has exceeded it's boundaries, the attacker places executable code in the overflow area which can then allow the attacker to execute their own sequence of instructions. This can result in arbitrary code being executed in system (privileged) mode which can allow the attacker to control the system.