IBM said on Wednesday it agreed to buy Internet Security Systems Inc. for $1.3 billion to beef up its product line in the rapidly growing business of Internet security. International Business Machines Corp., continuing an acquisition drive to fuel growth in its software and services businesses, said it will pay $28 a share for Internet Security, a 7.7 percent premium to its Tuesday closing price of $26.

Internet Security runs data centers that remotely protect businesses against Internet-based attacks. It is the only major player in that area.

Internet Security also sells software and hardware devices that companies can add to their computer networks to protect against Internet-based security threats.

Its primary rivals include Cisco Systems Inc. , Juniper Networks , McAfee Inc. and Symantec Corp.

Armonk, New York-based IBM said it plans to sell Internet Security's products as services through its global services unit and integrate its programs into its Tivoli software for managing far-flung information-technology systems.