BOSTON, Jan 18 (Reuters) - Symantec Corp. and McAfee Inc., the top two makers of security software for personal computers, lost market share after Microsoft Corp. launched a competing product, an analyst said on Thursday.

Smaller rivals such as CA Inc. and Trend Micro Inc. WS,  also took share away from Symantec and McAfee, said Chris Swenson, director of software industry analysis at research firm NPD Group.

Symantec's Norton software brand claimed 64.7 percent of the U.S. retail market for security suites in the fourth quarter of 2006, down from 76 percent in the same period of 2005, said Swenson, whose firm collects data on retail sales.

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