New G4S chief executive Ashley Almanza -- who took over in July after a security fiasco at the London 2012 Olympics -- outlined plans to sell, grow or restructure 35 units.
The firm has operations in more than 125 countries with a global workforce of 620,000 staff, of which about 45,000 are in Britain.
"G4S has strong fundamentals and these will be improved by changes to the way we manage the business," said Almanza in a company statement.
Almanza said the businesses earmarked for overhaul generate USD 641 million of revenues.
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G4S plans to use any funds raised to slash debts and fund expansion in emerging markets.
The restructuring was revealed one day after Britain's Serious Fraud Office (SFO) launched a criminal probe over allegations that G4S and rival Serco had overcharged the Ministry of Justice for electronically tagging offenders.
The investigation was opened after it emerged that the two companies had overcharged the government to the tune of tens of millions of pounds for monitoring people who had died, returned to prison, left the country, or had their tag removed.
The government announced a review in July of all contracts with the two firms following the findings of an audit by accountants PricewaterhouseCoopers.
The overcharging dated back at least to 2005, according to Justice Secretary Chris Grayling.
Back in 2012, G4S was embroiled in a major security fiasco at the London Olympics after the company failed to provide thousands of the guards it had pledged for the huge sporting event, forcing the government to draft in troops to fill the shortfall.