Symantec researchers have identified a new premium-rate SMS Android Trojan that modifies its code every time it gets downloaded in order to bypass antivirus detection. This technique is known as server-side polymorphism and has already existed in the world of desktop malware for many years, but mobile malware creators have only now begun to adopt it."
http://it.slashdot.org/story/12/02/0...every-download
