After three days of BlackBerry chaos, Channel 4 News answers the key questions still being asked by millions of the mobile phone firm's customers.

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Q. When did the service disruption start?

A. The first outages were reported on Monday across Europe the Middle East and Africa, spreading across the world to Latin America and Africa. BlackBerry's maker, Research In Motion, has confirmed to Channel 4 News that sporadic outages are now being reported in the US and Canada.

Q. What is the problem?

A. initially it appeared that the issue was with a switch at its servers in Slough. Unlike other mobile systems, email goes through BlackBerry's own servers which have experienced the problems.Users should not experience problems with making phone calls or texting.

Experts have told Channel 4 News that if users are having problems with text messaging this is possibly due to an overload of the system caused by users resorting to texting instead of email. It is unlikely RIM is to blame directly for the two issues.

RIM said: "The messaging and browsing delays ... were caused by a core switch failure within RIM's infrastructure," it said. "As a result, a large backlog of data was generated and we are now working to clear that backlog and restore normal service."

Q. How long will it last?

A. Although RIM has said over the past few days that it has fixed the issue, it is unclear when the problems will actually be resolved and the news that North American users are now experiencing problems does not bode well.

RIM has also been criticised for a failure to keep users informed of the problems with only sporadic communications via Twitter or lucky journalists. A request from Channel 4 News for a response to that criticism has so far not been answered.