Symantec Corp., one of the leading makers of software that detects computer bugs, agreed to buy Intel Corp.'s antivirus business for $18 million in cash. Symantec plans to meld its Norton AntiVirus technology with an antivirus system Intel has been developing for the last year. As part of the transaction, Intel will recommend Norton AntiVirus products to corporate customers and market them through its distributors. The purchase is part of Symantec's plan to integrate technology from different software makers in a comprehensive antivirus software package. It also gets Intel's 18,000 corporate customers to complement its large retail business as it vies with rival Network Associates Inc. for control of the software-protection market. In Nasdaq trading, shares of Cupertino-based Symantec rose 25 cents to close at $13.75; Intel shares fell $1.31 to close at $87.