Cyber threat 'Conficker', which gains unauthorised control of systems, has been detected in over 1.7 million computers, mainly at business organisations across the world, said a Microsoft Security Intelligence Report today.

"Conficker is one of the biggest security problems we face, yet it is well within our power to defend against. In the fourth quarter of 2011 alone, Conficker was detected on 1.7 million systems worldwide," Director of Microsoft Trustworthy Computing Tim Rains said in a statement today.

According to the report, quarterly detections of the Conficker worm has increased by more than 225 percent since the beginning of 2009.

The malware is known to exploit vulnerability on Windows XP-based systems that allows it to execute a malicious computer program code when file sharing option is enabled in a computer.

"In addition, Conficker disables several important system services and security products and also downloads arbitrary files," the report said.

While examining reasons behind Conficker's prevalence in business organisations, research showed that 92 per cent of its infections were a result of weak or stolen passwords.

The rest eight percent of infections exploited vulnerabilities for which a security update exists, the statement said.