3.9. Date and Time Dependency
Several viruses replicate only within a certain time frame of the day. Others refuse to replicate before or after a certain date. For instance, the W32/Welchia worm only attempted to invade systems until January 2004.
Another example is the original W32/CodeRed worm, which was set to kill itself in 2001. However, other variants of the worm were modified to introduce an "endless life" version without this limitation. The life cycle manager of worms is discussed in more detail in Chapter 10.