In Spidersilk the novel thieves made life difficult for Mark and his companions. Although the term thief usually refers to those who steal someone else's possessions, there is also other types of thieves. For instance, there are many environmental thieves in our world today, and an extraordinary amount of energy thieves, also known as energy vampires. You may have actually encountered a few of these thieves without even knowing. To learn more on energy thieves check out this page:

http://psychcentral.com/blog/archives/2013/11/14/how-to-avoid-being-drained-by-energy-vampires/