ACI Worldwide (ACIW) announced a first-quarter loss stemming from its February acquisition of the bank technology vendor S1.

ACI reported an operating loss of $2 million, compared to a gain of $1.6 million for the same quarter a year earlier.

Revenue increased 32%, to $138 million, compared to the first quarter a year earlier. The acquisition of S1 Corporation added $22.5 million in revenue in the quarter as of February 13, ACI reported.

"We had an important first quarter with strong organic financial performance with the completion of the S1 acquisition," said Philip Heasley, ACI's chief executive, in a conference call.

Total operating expenses for the quarter were $139.2 million, a 43% increase compared to $97 million in the first quarter a year earlier.

Excluding $15.0 million of one-time expenses from the S1 acquisition such as severance, ACI said its operating expenses increased $27.2 million compared to a year earlier.

The quarter's loss follows the contentious acquisition of S1. ACI made a hostile bid last summer for S1, which was then in merger talks with Fundtech Ltd. (now Fundtech Inc.). ACI's bid derailed that merger, and Fundtech ultimately merged with software provider Bankserv, owned by GTCR LLC, a Chicago private-equity firm, in a deal valued at nearly $400 million.