Malware reading

Malware is like an umbrella term used for all malicious software to fall under. Viruses, Trojans, worms, etc all fall under the umbrella of Malware. The Sans Six incident handling model was suggested by the reading as a way to handle malicious software. Under this model there are 6 steps, preparation, identification, containment, eradication, recovery and lessons learned. Preparation and identification are constantly happening. Since there are so many viruses they can be broken into 4 subgroups, memory based, target based, Obfuscation Technique Based and payload based.

My question would be what type of malware do you think is the easiest to protect against and what could do the most damage?

Article:  http://www.zdnet.com/article/yahoo-latest-at-kill-the-password-alter/

Yahoo is looking to do away with passwords and instead go with a login that sends a push notification to the phone of the account owner to approve or deny an attempt to access an account.