Vector Capital, a San Francisco private equity firm, has led a group of investors in an agreement to buy SafeNet Inc., an information security firm about $634 million.

Vector’s offer represents a premium of about 1.6 percent over SafeNet’s Friday closing price of $28.30.

SafeNet, of Belcamp, Md., won a contract last year to provide security for Swift, the international banking cooperative which reportedly permitted U.S.-government monitoring of its transactions. The company had revenues of $263 million in 2005.