The number of security vulnerabilities in Apple's OS X operating system has increased compared to last year. 

A study by security firm Kaspersky Lab identified a total of 60 security vulnerabilities in the first half of 2006, compared to 51 during the same period in 2005. 

Vulnerabilities affecting the core operating system had decreased, however, down from 38 last year to 24 this year.

Security problems affecting the Safari web browser, Mail application and Quicktime media player were responsible for the overall increase.

The increase in vulnerabilities in Safari and Mail could be used to launch attacks via the internet, the report warned.

The study also highlighted the emergence of the first Mac OS worm in February this year. Leap-A spread via the iChat instant messaging system disguising its self as a Jpeg image file. 

A further three exploits were discovered during February and another six in April.

The research concluded that, while users of Apple's operating system are relatively safe from attacks, they must not become complacent.

"Apple's small share of the global personal computer market has protected Macs from the unwanted attention of malware authors," said the report.

"However, this will change as Apple systems become more popular. Once critical mass is reached, more malware will undoubtedly start to appear.

"History shows that once vulnerabilities are identified, malware writers are never far behind."