E-commerce services provider Digital River Inc said on Thursday it entered into an agreement to be acquired by an investor group led by Siris Capital Group LLC for about $840 million.

The deal, valued at $26 per share in cash, is at a premium of almost 50 percent of Digital River's Thursday's closing price.

The agreement, approved by the board of Minnesota-based Digital River, includes a 45-day "go-shop" period during which the company can solicit alternative proposals, Digital River said on Thursday.

Siris will finance the deal with a combination of equity and debt, for which it has secured financing.

The companies expect the deal to close in the first quarter of 2015.

Morgan Stanley & Co LLC acted as financial adviser to Digital River, while Macquarie Capital (USA) Inc, Union Square Advisors LLC and Evercore Partners Inc are financial advisers to Siris.