Security software maker Symantec Corp's proposed purchase of Veritas Software Corp. should be supported by shareholders of both companies, a top investor advisory group said on Friday.

Symantec, the world's biggest security software maker, and Veritas agreed in December to join forces in an effort to blend security with data management. Shareholders of both companies are scheduled to vote on the deal on June 24.

The companies believe selling their products together will meet growing demand from customers for fewer software vendors and will help firms comply with new regulations requiring many types of data, including e-mail messages, to be archived and secured.

ISS said both companies had not quantified the revenue or market share opportunities their deal represents long term, "which means that shareholders are being asked to make a leap of faith and trust the vision of management."

Symantec's stock is down about 35 percent since news emerged in early December about a possible deal.

The companies have said they expect cost savings of about $100 million in their first 12 months as a combined entity.

Many investors have been concerned about slower revenue growth of the combined company, with Symantec's revenue seen slowing from growth of roughly 35 percent in 2005 to around 18 percent in 2006.