Content filtering software -- from five vendors -- is set to become freely available from July as part of the government's program to combat offensive online content.

The AU$93.3 million National Filter Scheme will see the vendors' software provided via free download from a government portal. The vendors will be determined by a request for tender issued last week.

The "late July" launch of the scheme, according to the request for tender, is the latest slip in its schedule. The scheme has been beset by delays since being announced by Communications Minister Senator Helen Coonan last year.

In the tender, the government provided more detail of the scheme, designed to alleviate what it cited as community concern over the ease with which children can access offensive Internet content.

Users will be able to download the filtering software from the government portal -- yet to be set up -- until 30 June, 2009. They can also choose to receive the product by mail.

The filters will also be available to public libraries within Australia.

Although free, the filters are not expected to be of lesser quality than their off-the-shelf versions.

"The Government's expectation is that [the] PC filter product supplied under the Scheme must be the same as those supplied in comparable markets to Australia, including in relation to the provision of patches and updates," the tender said.

"[They] must provide all customers who install their PC filter product under the Scheme with all patches."

The government would choose at least one product capable of blocking chat applications on the Mac operating system, as well as at least one for blocking the same applications on Windows, according to the tender.

The vendors would also be required to provide technical support to users of the filters until 30 June, 2010. Call centres capable of meeting expected demand must also be set-up before the launch date, said the tender.

Under the terms of the scheme, the government will cover the vendors' licensing and support costs. However, this would be reliant on the vendor's product achieving a minimum level of take-up from users, to be agreed by the government and vendor.

"Where a vendor does not achieve a critical level of take-up of their PC filter agreed between the Government and the vendor, the Government may withdraw the vendor from participation in the Scheme," said the tender.

The filters will only be available to Australian residents.

An advertising campaign will accompany the launch of the free filters.