Well he is really close to IEEE[1], so I think if there was any legalize involved, he must covered it. I follow professor Spinellis since 2008 and he seems to be a really nice guy who pays exceptional attention to details.
UPDATE: Apparently DSpinellis is the new editor in chief of IEEE software magazine[1].
The Author's allowed to do this. While the copyright assignment requires any commercial use to be licensed through the IEEE, any personal use, including putting it on a web page, is allowed.
Did the author obtain the permission from IEEE to publish this work on a publicly facing internet server?!