Source

U.S. customs authorities have assigned themselves the authority to copy all data on your laptop or other electronic device when you cross a U.S. border. I
wrote about this policy last year.

Now, customs authorities in Canada (and other countries, especially the U.K.) are getting into the act. I’ve received reports from several sources (among them from J. J. Luna,
author of the classic How to be Invisible) describing intimidating
encounters at the Canadian border. Luna reports that after being routed
into a secondary inspection queue, customs officials forced him to
reveal the passwords to his two laptops and USB flash drives. Then,
they disappeared with these devices in hand for nearly an hour,
presumably to copy and inspect them.

Your smart phone may be subject to the same type of inspection, and all your photos, text messages, online searches, and calling records copied onto a customs database.

To avoid a border inquisition, the best precaution is not to carry any electronic device across an international border. For most people, this isn’t practical, so the
next-best strategy is to carry only “sanitized” devices.

For instance, I have a laptop I use only for international travel. There’s nothing on it except for the operating system and program files. I also have an “unlocked” cell
phone I use only for international travel. When I arrive in a new
country I purchase a domestic SIM card from a local phone dealer. This
not only protects your privacy at the border, but also insures your
domestic carrier has no record of your international calls. And, it
eliminates roaming charges.

If you do carry your cell phone across the border, delete any photos or text messages you feel to be even remotely controversial, and then reset it to factory settings. You can
find instructions for doing so at http://www.master-reset.com.

What if you need access to confidential data while traveling internationally? One option is to upload a zip file containing your data to a commercial backup service, such as
Carbonite (http://www.carbonite.com).  Be sure to encrypt the data before uploading it, using a product such as PGP Whole Disk Encryption (http://www.pgp.com) or True-Crypt (http://www.truecrypt.org).

Another option is to send an encrypted USB flash drive to your destination via courier, and send it back via courier when you’re ready to return home. I’ve done this several times
without any problems.

If you must travel with confidential data across a border, you should encrypt all the data on your laptop or USB flash drive, including the hard disk itself, again using a program like PGP Whole
Disk Encryption or True-Crypt. However, customs officials may demand
that you decrypt any encrypted files before they allow you to proceed.
If you refuse, you might be detained until you agree to decrypt the
laptop for inspection. You could even be placed on a blacklist and
denied re-entry to that country.