@Sirmer,
Thank you for the feedback for all of us, and the heads-up for webmasters/developers out there.
Hack alert (Armorize) had the warning out for this since 09-2011.
Very good it is being detected. It is a mass WordPress infection going on,
read from Dean Edwards here: http://www.stopthehacker.com/tag/dean-edwards/
Sometimes malware is made up from two parts of innocent obfuscated script code and together with another piece of innocent code elsewhere on the website. It then becomes malicious code, when the two script code parts act together as malware.
As you may have read from the link I gave by Dean Edwards:
The injected PHP code causes your WordPress installation to load the malware located inside a file named “wp_inc/upd.php” (usually in your “/tmp” folder). The malware then builds an Iframe element pointing to one of many different websites.
This was/is being used as a mass infection hack. Good avast detects it and the shield blocks it,
Well this could help towards detecting, but there are good Dean Edwards packed and malicious Dean Edwards packed javascripts. With JS malware the main line of analysis is still being done manually - that is looking at the individual piece of malcode or recognizing a general attack sequence,
jsunpack and other tools can help towards de-obfuscation, but this deobfuscation is not needed if features are carefully extracted then obfuscated malicious code is found as easily (OCRF project - Eric Ching-Hao Ph.D),