Switzerland has frozen whatever assets Hosni Mubarak and his associates may have there, and anti-corruption campaigners are demanding the same of other countries. But experts say hunting for the deposed Egyptian leader's purported hidden wealth - let alone recovering it - will be an enormous task.

Mubarak's actual worth remains a mystery. A recent claim that he and his sons Gamal and Alaa may have amassed a fortune of up to $70 billion - greater than that of Microsoft's Bill Gates - helped drive the protests that eventually brought him down.

"Oh, Mubarak, tell us where you got 70 billion dollars!" protesters chanted in demonstrations before Egypt's ruler of 30 years was driven from office on Friday, and left Cairo for a gated compound in the Red Sea resort of Sharm el-Sheikh.

Forty percent of the country's 80 million people live on $2 or less a day, and critics accused officials of usurping the nation's wealth.

In recent days, watchdog groups and private lawyers have demanded that the country's chief prosecutor launch criminal investigations against the Mubaraks and some of their wealthy associates. Scores of former government officials have already been banned from travel and several, among them four former Cabinet ministers, have had their assets frozen.

How far these investigations will go ultimately depends on the political will of Egypt's leadership, said Eric Lewis, a partner with Washington-based law firm Baach, Robinson & Lewis, which specializes in international asset tracing and has done work in Kenya and Pakistan.

"What you often find is that while there's a kind of political impetus that seems to want to do it, the reality is that the real urge for transparency is more symbolic than real," Lewis said.

Far-reaching corruption probes could test the resolve of senior military officials who are running the country in the transition period. Some warn that a purge of Egypt's tycoons could make economic recovery from the political crisis more difficult.

Anti-corruption campaigners are calling for a speedy investigation and are urging countries other than Switzerland to freeze assets pre-emptively. "It's going to be a very difficult task, but in the interest of public money, things need to move now," said Omnia Hussien, Egypt expert at the advocacy group Transparency International.

The Mubaraks have never publicly discussed their assets. Hosni Mubarak's official monthly salary as president, counting benefits, came to 4,750 Egyptian pounds ($808), in 2007 and 2008, according to a Cairo think tank.

Rumors of hidden riches, such as expensive real estate in Britain, the United States and elsewhere, were fueled by the cozy ties between the Mubaraks and Egypt's business elite.