Encrypting everything

Until it is destroyed http://gizmodo.com/5912383/how-to-destroy-the-internet or we run out of resources to maintain it's cables, bridges, root servers and data centers, or some idiot replaces the current internet with a separate, strictly controlled panopticon-like global network, the web seems to be here to stay ... but it has an ad-hoc security model added post-hoc. Its up to us to make it better!?! WTF?

And there's a whole lot of information that we may not want other people to see:

Credit-card information
Social security numbers
Private correspondence
Personal details
Bank-account information
Medical health records
Other sensitive information

Also, see anonymising your traffic with linux and clean up all the things.

Using removable storage media

A simple but straightforward security method is to keep all sensitive information on removable storage media like portable flash memory drives or external hard drives that you only mount the device when you need access to it. You can turn old harddrives into external harddrives by taking them out of an old PC and putting them in a portable HDD USB storage kit (alias harddrive enclosure). These "DIY" kits are available for 2.5 inch and 3.5 inch HDD using either IDE or SATA connections and cost way less than a manufactured USB HDD.

You may have a permission problem accessing it. If so, change the group of /media/[externaldisk] to storage, change permissions to 775 and add users that need to be able to write to disk to the storage group (re-log required before changes are visible).

As root (or use sudo) do:

# chgrp storage /media/[externaldisk]
# chmod 775 /media/[externaldisk]
# gpasswd -a [user] storage

This way everyone will be able to read the disk, but only root and users in storage group will be able to write to it. If you want everyone to be able to read/write, use chmod 777. If the operation isn't permitted while running it as root you probably need to add support for the NTFS file system first:

# apt-get update
# apt-get install ntfs-3g

But the most popular forms of security all rely on encryption, the process of encoding information in such a way that only the person (or computer) with the key can decode it.

Cryptography

Before the digital age, the biggest users of cryptography were governments, particularly for military purposes. With the advent of the net we can all use it for:

Enabling authorized transactions.
Defending free expression.
Protecting our space, our objects and channels, from unauthorized access.
Collectively failing to put crypto into the hands of non-techie users.