lammert - 1:36 pm on Feb 4, 2010 (gmt 0)
As a programmer for many years, I would say that this software is extremely well engineered using one of the main vulnerabilities in modern large computer networks: upgrades and cleanups are implemented incrementally. As long as one computer in a corner of the company contains an infection, it will spread again over the complete network, even if all other computers have been cleaned or replaced. The only remedy is to replace the complete internal network infrastructure at once, without letting it communicate with old possible infected machines. And even then the network will only stay clean until one of the many weak parts in the chain called "human being" circumvents strict security rules and opens one infected email or visits one infected website.