A handful of internet firms have joined together to reduce the spread of adware and spyware which is distributed by 'piggybacking' on legitimate downloads.

The companies, including Yahoo, AOL and Verizon, have agreed to establish industry standards for monitoring and enforcing good behaviour on websites which offer downloadable software.

A new code of practice, maintained by independent online body TRUSTe, will ensure that sites offering downloads state clearly whether the software contains adware or trackware.

All co-operating sites will be required to inform the user of the types of advertising that will be displayed, and whether any personal information will be tracked and collected.

Sites will also have to warn users of any changes to PC settings, and users will need to opt in before the download can begin. Publishers must offer an easy uninstall procedure with clear instructions.

The participating companies are due to publish a 'white list' of certified applications. TRUSTe said that the programme will launch in beta form early next year.