Operating Systems Security
Needless to say, all operating systems are not created equal. None most popular operating systems of today were developed with secure electronic commerce in mind.
Unix is the oldest and most widely used networking operating system in use today. Unix has the advantage of having been hacked and patched by hackers and crackers for decades. One of the most popular Unix derivatives is Linux, developed by Linus Torvalds and now maintained by thousands of volunteers and many software companies. But Linux still has flaws that are being discovered every day. It is extremely important to monitor these occurances and apply the necessary patched when they are made available.
Microsoft's Windows platform has seen unprecidented growth as a server and client platform. Whether it be in the millions of home PCs, on the Internet or on corporate LANs, its popularity has caught the fancy of many hackers and virus writers.
Over the last decade, Apple's MacIntosh line of computers has been growing in popularity as users started getting fed-up with the complexities and security vulnerabilities often found in Windows. Mac OS X (or now just OS X), which is built on NeXT and BSD based Unix code has been secure so far but will see more attacks as it grows in popularity. Apple's iOS operating system for its iPads, iPhones, etc is also based on this code. On the mobile end, Google's (Linux based open source) Android operating system has seen one of the larges spikes in uptake ever and is based on an open architecture (vs iOS which is closed) makes the users have to balance out the additional control over their devices and OS with increase risk of acquiring malicious software.
Refer to the security resources page for more helpful links and ideas on securing operating systems.