Personally, its the removal of badware (Aka malicious software), so you get the idea. Spyware, trojans, adware, joke software, scareware... things like that. Programming comes second nature to me as it is sometimes required to take care of business. I also do not have a strong liking for those whom use what they know to exploit others, so there is that.
Oh, and as you have already noted, there really is always somthing new to learn, no matter how skilled you are.
malicious software removal is a good speciality. Particularly useful to many people, especially with so many individuals using what they know to exploit and harm others. Take this Sony hack - unprecedented.