Reverse-engineering experts say that malware writers are doing a better job hiding their code and making it difficult to crack. According to Adam Meyers, the director of cybersecurity operations at SRA International, more and more malware writers are scrambling whole blocks of their code and are using better obfuscation techniques to make it difficult to analyze and detect their code.

These techniques involve the use of better encryption or customized functions that make it difficult to reverse engineer the malicious code. For instance, some mobile malware uses DES encryption--an older data encryption standard--to scramble its data, Meyers said. Meanwhile, attackers are also using a variety of different ways to break into systems, experts say. Attackers that use social engineering attacks will utilize obfuscated Web addresses and code, while drive-by downloads will use encryption for the malware that is downloaded onto victims' computers when they visit certain sites.

In addition, attackers are using more direct methods for attacking servers to scramble the code and avoid being discovered by intrusion-detection systems, said Stonesoft Director of Product Management Matt McKinley.