A FREE software tool has been launched to let Irish internet users check if their PC has been infected with malicious software.

The software is available to download at botfree.ie. The website aims to inform computer users about the danger of botnets, to explain how to scan and clean computers of malware, and provide steps to prevent PCs from becoming infected again.

A botnet is a network of compromised PCs, or “bots” under the control of an unauthorised third party. Cybercrime gangs use botnets to steal money, send large volumes of spam e-mail or attack other websites.

It is not known how many computers in Ireland may be infected, but last week the FBI co-ordinated a major international operation to take down one of the largest known botnets of more than 400 million PCs in over 100 countries, including some in Ireland.

The IE-Cleaner scanning tool is designed to check PCs for infection. Computer owners are often unaware their machines are part of a botnet until they see the system’s performance slowing down.

The software is aimed primarily at computer users whose PCs don’t have anti-virus tools but is not intended to replace those packages. “There is no substitute for having up-to-date security software. What we are checking here is at a point in time,” said Aidan Ryan, technical adviser with the Department of Communications, Energy and Natural Resources which is supporting the scheme.

The intention is that many users will be prompted into downloading full security software after scanning their PC. The scheme is supported by Symantec, one of the largest security software providers, which is providing its technology for IE-Cleaner.

Technical support for IE-Cleaner will be provided from Germany, where the scheme was first launched last year. Other European countries are said to be planning similar initiatives.

Sven Karge from the German association of internet service providers, said the scheme had been very successful to date. About 25 per cent of PCs that had been scanned in Germany were originally infected with malware. A year on Germany had dropped from third to seventh place in the ranking of countries with malicious internet activity.

Paul Durrant, general manager of the ISP association of Ireland, said: “This is a constant problem ... we would welcome any initiative to ensure machines are being kept free from infection.”