Web server software and malware
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.
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