Security experts typically advise using Apple Inc. computers for sensitive tasks, such as online banking, because there are fewer viruses targeting the platform. But a new bug tears down one of Apple's major defenses.

The malware, a Trojan horse called Flashback.C, disables the Mac operating system's security update tool, Macworld reported Wednesday. The malware was discovered by the security company F-Secure.

The malware disguises itself as a Flash installer. "If you install the rogue software, it prompts you for your administrator password," the Macworld article said. "Enter that, and Flashback.C wipes out files necessary for" security updates.