The two companies have had a long-standing commercial relationship, and actually held talks aimed at “broadening” that relationship back in the summer of 2007, though those discussion went nowhere.

Big Blue first approached SPSS about a takeover in December last year, SPSS having earlier held unsuccessful acquisition and merger talks with two other unnamed companies.

IBM’s suggested per-share acquisition price was in the mid-$30s, however, and SPSS said discussions did not continue past this point.

The two companies remained in contact throughout the first quarter of 2009 regarding a potential business alliance. But in early April IBM’s managing director of corporate development Archie Colburn told SPSS chief Jack Noonan (pictured) that IBM was interested in making a purchase offer.

SPSS said Noonan had informed Colburn he did not believe the board would consider anything less than a price of $50 a share, but IBM’s proposal was in the range of $43-$44. As expected, the SPSS board was not interested.

IBM came back with a proposed price of between $48 and $50 a share, eventually settling on $50 after further negotiations.

According to SPSS, its financial adviser Bank of America Merrill Lynch held talks with other potential buyers and “engaged in further preliminary discussions with a limited number of selected third parties regarding their strategic interest” in the industry in which SPSS works.

“In connection with these broader discussions, in certain instances BofA Merrill Lynch discussed such third parties’ interest (or lack of interest) in an acquisition of SPSS,” the company said.

But the merger agreement precludes SPSS from actively soliciting alternative proposals, and even if a “superior proposal” were received, the company’s board of directors would not be permitted to terminate the agreement with IBM until a shareholder vote on the transaction has taken place. Also, SPSS is obliged to pay IBM a break fee of $23.5m if the agreement is terminated.

IBM’s purchase of SPSS is subject to approval by SPSS shareholders, applicable regulatory clearances and other customary closing conditions. It is expected to complete before the end of the year.

A handful of law firms have started investigating the deal, however. They are looking at whether the price of $50 a share undervalues SPSS and whether the company’s board could have squeezed more from any potential acquirer through an open auction process.