NEW YORK (CNN/Money) - Security software provider Symantec announced Thursday it is buying back-up and storage software maker Veritas Software in a stock deal worth about $13.5 billion.

The companies said that Veritas (Research) shareholders would receive 1.1242 shares of Symantec (Research) for each of their shares. Based on Wednesday's closing prices, that represents a premium of just less than 10 percent. But Vertitas' price is up 22 percent since the first press reports of the rumored deal earlier this week.

Upon closing, Symantec shareholders will own about 60 percent of the combined company, which will retain the Symantec name, with Veritas shareholders owning the rest. The transaction is expected to be tax-free to shareholders.

Symantec is a leading maker of security software under the Norton brand of products, used to protect computers against viruses and spam. Veritas makes data protection, storage and server management software and its products are used by 99 percent of the Fortune 500, according to the company.

"Customers are looking to reduce the complexity and cost of managing their IT infrastructure and drive efficiency with fewer suppliers," said a statement from Symantec Chairman and CEO John Thompson.

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It is the second major software merger announced this week. Monday Oracle announced it had reached a $10.3 billion cash deal with rival business software provider PeopleSoft, ending an 18-month hostile takeover battle for the company. Analysts have said they expect the trend of software mergers to pick up in the coming months.

"It's harder for niche vendors to survive and grow, and we'll see more and more of those guys getting bought," Jim Shepherd, a business software analyst with AMR Research, told Reuters earlier this week.