According to Computerworld's article "Researchers wait for Downadup worm's second act", this 'well-engineered' worm was written by hackers who know their stuff.
"This is a very well-engineered piece of software," said Alfred Huger, vice president of development at Symantec Corp.'s security response group. "It's very well thought out. Whoever wrote it, it's not their first time writing malware. It looks as if the author has had a great deal of experience writing software, and is fully versed in writing network-level code." Read the full article here.
This story, "Researchers wait for Downadup worm's second act" was originally published by Computerworld.