Bill Gates, the founder of computer software giant Microsoft, is to give away much of his fortune to charity.

Mr Gates, who owns 20% of Microsoft, is the world's richest man, with a fortune worth around $100bn (£65bn).

But according to his father, who manages the William H. Gates Foundation, he plans to donate the bulk of his holdings to the charity within his lifetime, making it the richest private charity in the world.

US businessmen have made a habit of philanthropic giving ever since Andrew Carnegie endowed the public library movement with the profits of his steel mills.

David Packard, the founder of computer company Hewlett Packard, has also left his shares to a charitable foundation, as did Henry Ford, the founder of the motor car company. Three of the world's top drug companies also have charitable trusts.

Fighting Aids

Mr Gates' father told the Sunday Times newspaper that his son had been shocked by the level of poverty and disease in developing countries.

It is expected that much of the money will be used to fund research on developing vaccines to combat diseases like Aids and malaria.

"A widely distributed vaccine can help make our goal of a world without Aids a reality. Melinda and I want our children - and all children - to grow up in a world without Aids," Bill Gates said.

The donation would make the Gates Foundation, which is already the fifth biggest charity in the world, far larger than medical charities like the Wellcome Trust.

Mr Gates and his family will not become penniless. He still plans to leave $10m (£6.5m) each to his two children, and lives in a $60m mansion near Seattle.

Controversy

Critics charge that the announcement is timed to deflect criticism from Microsoft's business practices.

The US Justice Department has charged that Microsoft has illegally tried to create a monopoly in the market in browsers which search for sites on the Internet, by 'bundling' its Internet Explorer software along with its Windows 95, forcing companies to buy both together.

The case is still awaiting judgement.

But Trevor Neilson of the Gates Foundation denied any link.

"Bill and Melinda have already endowed their foundation with $10bn .. they are doing this because they think it is the right thing to do," he said.