The Apple Macintosh, SCO Unix, and Hewlett-Packard Tru64 Unix operating systems are the platforms least prone to hacker attacks and damages from viruses and worms, according to a study released Thursday by security firm mi2g.

Most vulnerable? Not surprisingly, it's Microsoft Windows, which was affected by most of the known security vulnerabilities announced this year, 44% of them, followed by Linux at 19%; BSD, 9%; and Sun Solaris, 7%. Only 0.5% of the vulnerabilities announced in 2002 affected SCO Unix, and 1.9% each affected Mac OS and Compaq Tru64 systems, the report says. The remaining 17% of vulnerabilities affected a variety of other systems.

This year has been the worst on record for overt digital attacks, with 57,977 attacks to date, the report says. Microsoft Windows suffered the highest percentage of overall attacks, 54%, followed by Linux, with 30%; BSD, 6%; and Solaris, 5%.

The Mac OS suffered only 31 overt digital attacks, 0.05% of the total, even though Apple has about 3% of the world computer market share. SCO Unix suffered 165 attacks, 0.2%, and Tru64 suffered 10 attacks, 0.02%. The remaining 5% of attacks affected other operating systems.