However, ISS's full range of network security products makes little sense for IBM, especially because the company appeared to have walked away from the segment a few years ago, Pescatore said. "IBM is really strong in the ID and access management side of security, and that is totally different from network security."

With the ISS purchase, IBM will find itself suddenly in competition with well-established vendors of network security products, including Cisco Systems Inc., Enterasys Networks Inc. and Juniper Networks Inc., Pescatore said. "It just doesn't make sense for IBM."

IBM's move fits with its enterprise services and business process outsourcing focus, said Jon Oltsik, an analyst at Enterprise Strategy Group Inc. in Milford, Mass. "The Proventia stuff is sort of a throw-away in this deal," he said. "Other than the existing installed base, it is a small piece of the deal."

Some ISS customers are likely to be upset at the company's "loss of independence as a stand-alone vendor," Stamp said. "There are some who are likely to have chosen ISS because they valued their independence from a larger company whose No. 1 priority maybe isn't necessarily security."

Upon completion of the deal, ISS's operations will become a business unit in IBM's Global Technology Services business. The company's software products will be integrated with IBM's Tivoli management suite, Rahmani said.