Web Server Software and Malware

Tuesday, June 5, 2007 9:30 AM

Posted by Nagendra Modadugu, Anti-Malware Team

In this post, we investigate the distribution of web server software to provide insight into how server software is correlated to servers hosting malware binaries or engaging in drive-by-downloads.

We determine server operating system by examining the 'Server:' HTTP header reported by most web servers. A survey of servers running roughly 80 million domain names reveals the web server software distribution shown below. Note that these figures may have some margin of error as it is not unusual to find hundreds of domains served by a single IP address.

Web server software across the Internet.

Web server software distribution across the Internet.

Our numbers report a slightly larger fraction of Apache servers compared to the Netcraft web server survey. Our analysis is based on crawl information and only root URLs were examined, therefore hosts that did not present a root URL (e.g. /index.htm) were not included in the statistics. This may have contributed to the disparity with the Netcraft numbers.

Amongst Apache servers, about 35% did not report any version information. Presumably the lack of version information is considered to be a defense against version specific attacks and worms. We observed a long tail of Apache server versions; the top three detected were 1.3.37 (15%), 1.3.33 (7.91%), and 2.0.54 (6.25%).

Amongst Microsoft servers, IIS 6.0 is by far the most popular version, making up about 80% of all IIS servers. IIS 5.0 made up most of the remainder.

Web server software across servers distributing malware.

We examined about 70,000 domains that over the past month have been either distributing malware or have been responsible for hosting browser exploits leading to drive-by-downloads. The breakdown by server software is depicted below. It is important to note that while many servers serve malware as a result of a server compromise (by remote exploits, password theft via keyloggers, etc.), some servers are configured to serve up exploits by their administrators.

Web server software distribution across malicious servers.

Compared to our sample of servers across the Internet, Microsoft IIS features twice as often (49% vs. 23%) as a malware distributing server. Amongst Microsoft IIS servers, the share of IIS 6.0 and IIS 5.0 remained the same at 80% and 20% respectively.

The distribution of top featured Apache server versions was different this time: 1.3.37 (50%), 1.3.34 (12%) and 1.3.33 (5%). 21% of the Apache servers did not report any version information. Incidentally, version 1.3.37 is the latest Apache server release in the 1.3 series, and it is hence somewhat of a surprise that this version features so prominently. One other factor we observe is a vast collection of Apache modules in use.

Distribution of web server software by country.

Web server distribution by country

Malicious web server distribution by country

The figure on the left shows the distribution of all Apache, IIS, and nginx webservers by country. Apache has the largest share, even though there is noticeable variation between countries. The figure on the right shows the distribution, by country, of webserver software of servers either distributing malware or hosting browser exploits. It is very interesting to see that in China and South Korea, a malicious server is much more likely to be running IIS than Apache.

We suspect that the causes for IIS featuring more prominently in these countries could be due to a combination of factors: first, automatic updates have not been enabled due to software piracy (piracy statistics from NationMaster, and BSA), and second, some security patches are not available for pirated copies of Microsoft operating systems. For instance the patch for a commonly seen ADODB.Stream exploit is not available to pirated copies of Windows operating systems.

Overall, we see a mix of results. In Germany, for instance, Apache is more likely to be serving malware than Microsoft IIS, compared to the overall distributions of these servers. In Asia, we see the reverse, which is part of the cause of Microsoft IIS having a disproportionately high representation at 49% of malware servers. In summary, our analysis demonstrates how important it is to keep web servers patched to the latest patch level.

The comments you read here belong only to the person who posted them. We do, however, reserve the right to remove off-topic comments.


solrac said...

The study should include the distribution of the 70000 domains in the total number. This would show if the conclusion is fair enough with the web server investigation.
This only true if it follows a normal distribution and a representative subset.

ChrisTorng said...

I think the point of patch is totally wrong.

First, by my knowledge, pirated Windows still can get Automatic Update automatically download patch, they just can't go to Windows Update/Microsoft Update/Microsoft Download Center site for manual update. So almost all Windows can get all the required security patch.

Second, I don't think that all malicious is caused by hacking into an unpatched Windows. Maybe the user accidently open an attachment and install some trojans. So the user's computer become a malicious web server through the control of trojan from hacker, not through break into an unpatched security hole. So I think some IIS rate of China and S. Korea is contributed from the many hackers from those country, sending trojan mails with their familiar language to their people. So the count of China and S. Korea just reflect the fact that the hackers from these country is more then other country.

Third, I think that the count is by IP/domain name. I think hackers also host the malicious web server by themself. They get many IPs and domain names to point to a single web server to avoid detection/blocking. So the count of web server cannot see as so much individual web server. Maybe the hackers from China and S. Korea/Russia is familiar with IIS/Apache, so they contribute many many counts by physically single IIS/Apache.

The last, most people who install Apache because he/she want to populate a web site. He/she should open their site often. If there are any problem they will know at first time and try to clear them. But many people who install IIS just because Windows install and enable it by default. (I have forget which Windows version will do that) They never open the site on localhost, they even don't know they have a web site on their computer. So they don't know their IIS is used for distributing malware. The malicious IISs live for a long time, so the statistics show that the rate of malicious IIS is more then the rate of all IIS.

benny said...

Ermm I'm kinda new to blog but anyway what the heck.. In my own opinion Apache is much safer compared to IIS, and why am i saying so?? Because it's M$ own fault for causing so. M$ detected in IIS 5.0 there's a loophole that allow hacker to exploited it and it provides the technical details to all to view on where and how to actually exploit the loophole (which in my own term is pretty idiotic). And at the same time no patch or solution was provided (ain't that is similar to blowing off your own whistles).. And the solution provided is nothing much just as usual,: Please upgrade to a updated version of M$ products IIS 5.0 to IIS 6.0 (hey!! IIS 6.0 wasn't optimized for WinXP/2000 initially, only Win2003 Servers), WinXP to Vista blablabla (why can't I remain wih my legacy systems which I pretty comfortable with, and where the heck is my patch?? M$, YOU found it then give me the solutions or workaround to the loophole not just telling me Yeap!! OUR product is faulty so live with it; in which I can't, sorry).. That's why Apache is better position, at least if there a loophole detected, though no patch is provided, some tweakers might have some ideas on setting the pace right unlike M$, huh!! 1 billion dollars on research, what a waste.. I started to doubts the IQs of M$ software engineers.. Sigh, geniuses Yeah MY @SS

Rosyna said...

I too agree some of these malware spreading IIS servers may have been infected via another means (like a trojan) and the malware turned on the IIS service to infect others/do other evils.

It's a lot like spam botnets.

Bob said...

It is worthy to note that the reason for the disparity of IIS in South Korea is likey due to the tiein that S Korea has into Microsoft OPerating Systems. More details here:


Makes intresting reading. Tied into the fact that S Korea has a large propensity for Bots which is not just due to their runnig MS products but also due to the large amounts of available bandwidth. It would be intresting to know how many of the compromised servers were home based machines or hosted.

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krish said...

Given the stats in this article though not a complete survey, but the figures certainly hints to the growing concern i.e the objective of the world wide web is getting contaminated from every parts of the world.

root123 said...

Software Development Company The study is a remarkable step in highlighting one of the core issues that the web is facing today

Jeremy said...

I knew that Apache was leading the way in the web server community but I did not realize the extent to which IIS and other windows web servers were trailing the hosting industry.

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Thanks for the information. How can I protect visitors on my site? I am providing plain text content through html pages. But still are there any ways through which I can curb misuse.

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alastairc said...

It would be useful for any followup if you could distinguish between those who are victims of hacked servers compared to those who are intentionally distributing malware.

This could of course be impossible to detect reliably, but I'd still love to know...

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Sweety said...

Hi Nagendra,
Your study on web server software & malware is quite impressive. It would be more helpful if you suggest any good solution to this problem..

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Once a bank has been alerted to the fact that it is the subject of a phishing attack, the race is on to close the target phishing site as quickly as possible. However, professional fraudsters will take steps to ensure that the process is as difficult and time consuming as possible: your time is their money.

Fraudsters will often host their sites in developing countries with limited law enforcement resources and incentivize the hosting company to keep the site running as long as it possibly can. Indeed, some unscrupulous hosting companies actually promote fraud hosting as a service.

Netcraft’s countermeasures service helps banks and other financial organizations to combat these techniques. Once a phishing site has been detected, Netcraft responds with a set of actions which will significantly limit access to the site immediately, and will ultimately cause the fraudulent content to be eliminated.

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Integrated Business Software said...

Very interesting article. Good research, and I like the graphs.

Amrit Ray said...

Yes, it is quite interesting to see the distribution of server software across different countries and the percentage of these servers software hosting malware. It is true that across Asia most people are inclined towards IIS rather than other operation systems. The amount of piracy that goes on here is tremendous and due to this auto update of the server does not happen and they become a target for hosting Malware, especially in a shared hosting environment. Original software can lower the percentage substantially. Web Designer.

Aparna said...

Thanks for this interesting post.

suparna said...

thank you for sharing such an informative post, good research.

Mazhar Hussain Shah said...


It is very interested topic about to the distribution of the web server software.I think in this way the people can get a a lot of useful information about to the web server,For example,How many domain are attached to th web server,So it approximately 80 million.
Thanks again for this useful information.
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Mainul said...

Thats a great statistics about different HTTP servers and their comparative performance. Realy uncommon resource. Web Design UK

PierreG said...

Nobody mentioned the fact that IIS 6/7 is nested into the Window kernel (to run faster than others).

When a vulnerability is exploited in the kernel, attackers have full access to the highest privileges.

This is not the case with user-mode web servers.

More details on this issue here:


By the way, IIS 7.0 is no longer the fastest web server under Windows (despite the kernel), see:


Rohit Tripathi said...

I think you have to view numbers in comparison to the total number of web
servers using Apache and IIS. As you can see in the graph which can be
found a bit higher, a lot more web servers are using Apache than IIS. If
actually the absolute number of malware distributing IIS servers is
equals to the number of Apache, the relative numbers are much worse for

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LeadZoomer said...

Thanks for posting very useful post. Now days there are numbers of Pirated Windows Software available and most of them doesn't have automatic update option to download patch.

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Zaibunnisa Faisal said...

I am getting this "Sorry" message more and more often now. I do not believe that there is any "worm" in my system and it is a real nuisance. It is forcing me to switch to Yahoo or Ask. I do all my searche by hand and they are very innocent searches too. The sorry message does not even end with a CAPTCHA thingy to put my verification code to prove I am human. This is seriously getting on my nerves! I never had this problem before. Its only started recently, but I have no idea what triggered it.

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Goa Ad said...

it seems thats there is a lot to be done for protecting users from various exploits. Many antiviruses do not recognize or provide protection against web malwares.