Xero’s security policies are modelled on those used by the Banks.  They use 128 bit SSL encryption, the same used for internet banking, and their servers are hosted on a tier-one hosting provider who monitors their servers and firewalls 24/7/365 at a guarded facility.

They use an external organisation to continually audit their security by conducting penetrative testing, unannounced and deliberate attacks to measure their vulnerability to outside hackers.  Data is stored on their secure servers and backed up regularly, so even if your computer is lost or stolen your data is safe.