Bill Gates, the co-founder of software giant Microsoft, has increased his stake in UK's G4S, which is the biggest security firm in the world.

The firm's reputation has been tarnished due to errors relating to the staffing of the London 2012 Olympics. However, the company is now looking to revive its presence it's the market. The Bill & Melinda Gates Foundation Trust and Cascade Investment, which is a Gates-owned management firm, increased its stake in G4S to 3.2 per cent during the previous week after acquiring 6 million more shares in the company. The Bill and Melinda Gates Foundation was founded in 2000 and has investments in a range of firms around the world from banks to railway networks.

G4S offers services including cash transportation and prison management and has presence in more than 125 countries around the world. The company faced trouble when it was not able to provide promised 10,400 guards for the Mega gaming event in London. The company's chief executive stepped down in the previous month following concerns over profits.

The shares of G4S fell 1.2 per cent to 241.55 pence on Monday. The shares have fallen by 18 per cent in three months.