The German government warns that several Apple devices such as the iPhone and iPad have two critical security weaknesses that cannot be remedied by any patch in existence.

The country's federal office for information security warns against Apple mobile devices, saying that users should only visit websites they deem trustworthy and refrain from opening PDF files until Apple releases a fix.

"This allows potential attackers access to the complete system, including administrator rights... It has to be expected that hackers will soon use the weak spots for attacks," the agency said in a statement.

The company said it is investigating reports of vulnerabilities for the iPad, iPod Touch and iPhone.

The potential vulnerability involves Safari, the mobile Internet browser, and the way it opens PDF files in Apple's iOS software. The vulnerability received attention with JailbreakMe, a browser-based service launched by US-based hackers that allow users to unlock Apple devices from restrictions imposed by the manufacturer.

The German government's advisory involves iPhones using iOS versions 3.1.2-4.0.1, iPads using iOS 3.2-3.2.1 and the iPod Touch using iOS 3.1.2-4.0.