"Over the past two years, we had found one or two pieces of malware targeting Macs," said Patrik Runald, a security researcher in the San Jose, Calif., office of F-Secure Corp. in Helsinki, Finland. "Since October, we've found 100-150 variants."

The rising security threat could hurt Apple, which has long touted the security advantages of its platform over those of Microsoft Corp. (NASDAQ:MSFT), whose software is a perennial hacker target, The Financial Times reported.

Also targeted are Apple's iTunes digital media players and iPhone Web-enabled multimedia cell phones, F-Secure said in a report.

"Unlocking" iPhone security controls, an increasingly popular activity, adds to the phones' vulnerability, the report said.

Apple would not discuss any steps it was taking to counter the growing number of attacks, The Financial Times said.

But Apple said, "We take security very seriously and have a great track record for addressing vulnerabilities before they can affect users."