Although the actual number of versions is unknown, it is estimated to be well into the thousands.
This briefly held the record for most variants, but has subsequently been surpassed by the Agobot family.
As a result of having so many variants, one antivirus company is often not able to recognize and remove all versions of the worm.
Early detection of the Spybot worm usually comes from network engineers detecting the Denial of Service attack generated when the worm tried to communicate back to various IRC channels.
Hackers will occasionally use the worm to make easy-access programs for FTP & IRC channels