Security Changes Everything



Watts S. Humphrey

This library item is related to the following area(s) of work:

Process Improvement

This article was originally published in News at SEI on: February 1, 2006

The last column began a discussion of software quality. It stressed the growing importance of security as a motivating force for software quality improvement and noted that the recent Sarbanes-Oxley Act is changing management’s attitudes about software security and quality. The quality of today’s software products falls far short of what is needed for safe and secure systems. We can no long afford to power our critical corporate and national infrastructure with defective software. Since security is such an important concern for many businesses, the pressures for improvement will almost certainly increase.

In this column, I discuss why software quality has not been a customer priority in the past and how that attitude has influenced the quality practices of our industry. I then discuss the changes we will likely see in these quality perceptions and what our customers will soon demand. Finally, I describe the inherent problems with the test-based software quality strategy of today and why it cannot meet our future needs. In the next column, I will outline the required new quality attitude and the prospects for success in our quest for secure and high-quality software.

The Quality Attitude

Even though current industrial-quality software has many defects, quality has not been an important customer concern. This is because even software with many defects works. This situation can best be understood by examining the “Testing Footprint” in Figure 1. The circle represents all of the possible ways to stress test a software system. At the top, for example, is transaction rate and at the bottom is data error. The top left quadrant is for configuration variations and the bottom left is for the resource-contention problems caused by the many possible job-thread variations in multiprogramming and multiprocessing systems. At the right are cases for operator error and hardware failure. The shaded area in the center represents the conditions under which the system is tested.

Since software systems developed with current industrial quality practices enter test with 20 or more defects per thousand lines of code, there are many defects to find in test. Any reasonably well-run testing process will find and fix essentially all of the defects within the testing footprint. If this process is well designed, if it covers the ways most customers will use the system, and if it actually fixes all the defects found, then, as far as these users are concerned, the system would be defect free.

Trying Harder

While current quality practices have been effective in the past, this test-based quality strategy cannot meet our future needs for three reasons.

First, testing is a very expensive way to remove defects. On average, it takes several hours to find and fix each defect in test and, because of the large numbers of defects, software organizations typically spend about half of their time and money on testing.

Figure 1: The Testing Footprint

Figure 1: The Testing Footprint

The problem is that testing is being misused. Even with all the time and money software organizations spend on testing, they still do not produce quality products. Furthermore, the evidence is that even more testing would not produce significantly better results. The problem is not that testing is a mistake. Testing is essential, and we must run thorough tests if we are to produce quality products. In fact, testing is the best way to gather the quality data we need on our software products and processes.

The second reason that testing cannot meet our quality and security needs stems from the nature of general-purpose computers. When these systems were first commercially introduced, the common view was that only a few would be needed to handle high-volume calculations. But the market surprised the experts. Users found many innovative applications that the experts had not imagined. This user-driven innovation continues even today. So, in principle, any quality strategy that, like testing, requires that the developers anticipate and test all the ways the product will be used simply cannot be effective for the computer industry.

The third reason to modernize our quality practices is that we now face a new category of user. In the past, we developed systems for benign and friendly environments. But the Internet is a different world. Our systems are now exposed to hackers, criminals, and terrorists. These people want to break into our systems and, if they succeed, they can do us great harm.

The reason this will force us to modernize our quality practices is best seen by looking again at the figure. Since the test-based quality strategy can find and fix defects only in the testing footprint, any uses outside of that footprint will likely be running defective code. Since over 90% of all security vulnerabilities are due to common defects, this means that the hackers, criminals, and terrorists have a simple job. All they have to do is drive the system’s operation out of the tested footprint. Then they can likely crash or otherwise disrupt the system.

One answer to this would to be to enlarge the tested footprint. This raises the question of just how big this footprint can get. A quick estimate of the possible combinations of system configuration, interacting job threads, data rates, data errors, user errors, and hardware malfunctions will likely convince you that the number of combinations is astronomical. While there is no way to calculate it precisely, the large-system testing footprint cannot cover even 1% of all the possibilities. This is why modern multi-million line-of-code systems seem to have a limitless supply of defects. Even after years of patching and fixing, defect-discovery rates do not decline. The reason is that these systems enter test with many thousands of defects, and testing typically finds less than half of them. The rest are found by users whenever they use the system in ways that were not anticipated and tested.

The Quality Requirement

Indeed, “security changes everything.” Software pervades our lives. It is now common for software defects to disrupt transportation, cause utility failures, enable identity theft, and even result in physical injury or death. The ways that hackers, criminals, and terrorists can exploit the defects in our software are growing faster than the current patch-and-fix strategy can handle. With the testing strategy of the past, the bad guys will always win.

It should be clear from this and the last column that we must strive to deliver defect levels that are at least 100 times better than typically seen today. Furthermore, we need this for new products, and we must similarly improve at least part of the large inventory of existing software. While this is an enormous challenge and it cannot be accomplished overnight, there are signs that it can be done. However, it will require a three-pronged effort.

First, we must change the way we think about quality. Every developer must view quality as a personal responsibility and strive to make every product element defect free. As in other industries, testing can no longer be treated as a separate quality-assurance or testing responsibility. Unless everyone feels personally responsible for the quality of everything he or she produces, we can never achieve the requisite quality levels.

Next, we must gather and use quality data. While trying harder is a natural reaction, people are already trying hard today. No one intentionally leaves defects in a system, and we all strive to produce quality results. It is just that intuition and good intentions cannot possibly improve quality levels by two orders of magnitude. Only a data-driven quality-management strategy can succeed.

Finally, we must change the quality attitude of development management. While cost, schedule, and function will continue to be important, senior management must make quality THE top priority. Without a single-minded drive for superior quality, the required defect levels are simply not achievable.

Stay tuned in, and in the next column I will discuss the required quality attitude.


In writing papers and columns, I make a practice of asking associates to review early drafts. For this column, I particularly appreciate the helpful comments and suggestions of Marsha Pomeroy-Huff, Julia Mullaney, Dan Wall, and Alan Willett.

In closing, an invitation to readers

In these columns, I discuss software issues and the impact of quality and process on developers and their organizations. However, I am most interested in addressing the issues that you feel are important. So, please drop me a note with your comments, questions, or suggestions. I will read your notes and consider them when planning future columns.

Thanks for your attention and please stay tuned in.

Watts S. Humphrey

About the Author

Watts S. Humphreyfounded the Software Process Program at the SEI. He is a fellow of the institute and is a research scientist on its staff. From 1959 to 1986, he was associated with IBM Corporation, where he was director of programming quality and process. His publications include many technical papers and several books. His most recent books are Introduction to the Team Software Process (2000) and Winning With Software: An Executive Strategy (2002). He holds five U.S. patents. He is a member of the Association for Computing Machinery, a fellow of the Institute for Electrical and Electronics Engineers, and a past member of the Malcolm Baldrige National Quality Award Board of Examiners. He holds a BS in physics from the University of Chicago, an MS in physics from the Illinois Institute of Technology, and an MBA from the University of Chicago

The views expressed in this article are the author's only and do not represent directly or imply any official position or view of the Software Engineering Institute or Carnegie Mellon University. This article is intended to stimulate further discussion about this topic.

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