NEW YORK (CNN/Money) - Despite new efforts to make telephone networks more secure in case of terrorist attacks and natural disasters, network outages are growing more severe and taking longer to repair, said a news report Thursday.

Over the past four years, the median duration of network outages was 3.3 hours, a rise from 2.86 hours during the eight years prior, according to the Wall Street Journal.

The severity of the outages, a number that takes into account the number of phone customers affected, is also up, said the Alliance for Telecommunications Industry Solutions.

However, the total number of network outages is down significantly in recent years -- by 50 percent since 2000.

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