Apple has agreed to mend a security defect in iPhones and iPads which enables viruses to install on devices.

IT security firm of Germany has cautioned that iOS of Apple- the operating system that executes the iPhone, iPad and iPod touch- has a ‘critical weakness’ that permits hackers to execute suspected code.

The German Federal Office for Information Security (BSI) told that opening a suspected PDF on an iOS device would permit unsafe programs to execute on the device.

An Apple spokesperson said: “Apple takes security very seriously, we’re aware of this reported issue and developing a fix that will be available to customers in an upcoming software update.”

The BSI informed that no attack has yet been done but cautioned: “Possible attack scenarios for cyber-criminals include the reading of confidential information (passwords, online banking data, calendars, e-mail content, text or contact information), access to built-in cameras, the interception of telephone conversations and the GPS localization of the user.”

BSI cautioned, in a declaration on its site (in German), against opening PDFs from unidentified sources until Apple mends the defect. It told that any device executing iOS version 4.3.3, the latest version will be affected.

The coming software update of Apple is iOS 5, will be launched in September. If, Apple thinks that the crisis is serious, it may launch security update earlier.