Worldwide threats from malicious software that cripple computers with spy programmes, viruses and worms have increased 43 percent over the past year, Microsoft said on Monday in its Security Intelligence Report.

The software giant said that the rise occurred despite a significant improvement in the security of its operating systems, as hackers targeted individual programmes and naive users.

Microsoft said that 90 percent of new vulnerabilities over the past year targeted programmes, while only 10 percent honed in on operating systems.

The report indicated that malware infection rates are generally higher in developing countries than in developed ones. Infection rates range from 1.8 for every 1,000 computers in Japan to above 76.4 for every 1,000 in Afghanistan.

The US had an infection rate of 11.2 infected computers for every 1,000 scanned - an increase of 25.5 percent in the last six months.

Microsoft recommended a number of protective steps that computer users should take: Checking for security updates from Microsoft and third-party software providers, installing up-to-date firewalls and antivirus and anti-spyware programmes, and exercising extreme caution in opening links and attachments embedded in emails, even if the email is from a trusted source.

These links can direct users to phony websites in a technique called phishing, which then combs users' computers for sensitive information.

China has the highest rate for these so-called browser-based exploits which comprised 46.6 percent of all security incidents there, compared to 23.3 percent in the US, Microsoft said.