Ok so they use what's called packers to not only obfuscate the malware code to bypass signature based A/V but also hide inside other binaries or Dll's to further evade heuristic defenses.  Then a reverse encrypted tunnel for control of infected machine was routed over normal HTTPS also undetectable by IDS.  It was to dynamic dns domains such as yahoo1.dyndns.org.  Reverse meaning it connects back to the attacker to allow ssh like access to the compromised host via the trojan.<p>There are all extremely advanced (but known) evasion steps for a very targeted attack.  It's rare to see all of them successfully used in one attack because of the complexity and skill required.