Free Technology for Teachers: Do the Two Step to Protect Your Google Drive, Dropbox, and Box Files | Using Google Drive in the classroom |

"The potential problem with cloud storage, and any other online service for that matter, is having your account compromised. One way to make it more difficult for your account to be compromised is to enable two-step authentication."

[Phishing from gmail accounts is very common so this is a worthwhile precaution if you are using Google Docs - GC]