The reasons for a software breakdown which resulted in no service for millions of Israeli mobile phone users last week are still unclear. Computer experts are worried that this could have been a successful trial run ofa cyber attack against Israel.

Cellcom, the largest mobile phone provider in Israel, experienced last Wednesday what the company described as a "failure in the heart of our system". For over 12 hours, most of the company's 3.3 million users were without service but, despite resuming normal operations, the company has been silent as to the causes.

According to some reports, the cause may have been maintenance work on the day before the breakdown, but sabotage is possible. Boaz Dolev, a former head of the government's internet service and now a consultant on computer security to the private sector, said that "the breakdown has the hallmark of an outside cyber-attack".

Israeli experts believe hostile countries may be targeting private communications firms that do not have the same level of software protection as the national infrastructure companies.