I work for HP in the area of security systems. Highlighted Tasks: Hardening / Pentesting OS: Linux, Wintel (2003-2012) DB (Oracle, SQL Server), IIS, Apache, etc.
Hardening, is usually the process of securing a system by reducing its surface of vulnerability, not only for OS, it include applications and services.
Vulnerability scan, not only focus on search vulnerabilities, but also fix them when it find them.
Pentesting, using own, third-party and open source tools for break the security.