Apple Mac computers, long touted for their resilience to online attacks, are becoming increasingly vulnerable to computer hackers, according to a new report.

Security analysts detected the first piece of malicious code to specifically target Apple computers last year and say the number of malicious programmes has increased dramatically in recent months.

The rising security threat could present a challenge to Apple, which has long touted the security advantages of its platform over those of Microsoft, whose software is a perennial target for hackers.

Apple declined to discuss specific steps it was taking to counter the growing number of attacks. However, Apple said: “We take security very seriously and have a great track record for addressing vulnerabilities before they can affect users.”

F-Secure said the surge in Mac attacks appeared to be the work of a single gang of professional hackers, known as the “Zlob gang”, which writes programmes that trick computer users into installing malicious software purportedly for viewing video files.

The increase in Mac-specific attacks comes as the number of viruses and other malicious computer programmes doubled from 2006 to 2007, according to F-Secure.