S1 Corp. said that it plans to repurchase up to 4 million more shares, and that a director installed at the behest of an activist investor group has resigned.

The Norcross, Ga., banking technology vendor said Wednesday that its board approved the increase to an existing buyback plan.

The purchases will be made with available cash whenever the company decides market conditions are right, S1 said.

Jeff Smith, the director who resigned, spent two years on the board. He is a managing director of Ramius Capital Group LLC of New York, which said in 2006 that it was part of an investor group that had acquired 9.2% of S1's shares and was pressuring the company to change its strategy.

Ramius initially urged S1 to sell itself. In May 2006 it added Mr. Smith to the board, and three months later it sold its Financial Reporting Solutions to Carlyle Group of Washington and Kennet Partners Ltd. of London for $38 million.

"At this time there are other opportunities which are demanding more of my attention, and S1 is in extremely capable hands," Mr. Smith said in a press release.