Bits of Africa are still quite dangerous. Tourists are advised not to travel without an armed guard.
I know a few people who've been stopped at gunpoint there. It's not usually an issue providing you give the gunmen what they want (usually money for drugs).
Lots of houses/compounds in Niarobi, Kenya for example have armed security, either on-site, or on-call.
Given Ethiopia's emergence as the US's 'new best friend' in the area (e.g. Somalian intervention), would it be too paranoid to assume some attempt by interested parties to drive a wedge between Ethiopia and the West (I know we're talking Brits not Yanks but when opportunity knocks...) or just old fashioned banditry?