Read this article at http://www.wired.com/threatlevel/2013/02/electronics-border-seizures/ about how the Department of Homeland Security (DHS) can seize and search your electronic devices at the border without cause. The border as defined by DHS extends 100 miles inland from the physical US border.
How long can they keep your devices? It’s not really defined, although according to the Electronic Frontier Foundation (EFF), devices are usually return within 5 days. How long can DHS keep your data and what can they do with it? Again, according to the EFF, procedures are not clear for handling sensitive or confidential data.
If you need to travel with electronics, the EFF has a guide on how to “make your data less vulnerable at the border” at https://www.eff.org/deeplinks/2010/11/effs-guide-protecting-devices-data-border. Always make sure that you back up your data before traveling, just in case any of your electronic devices are confiscated, lost, stolen, or damaged.
If you value your privacy, the EFF website is worth reading on a regular basis.
Intentional Privacy 