It's buried halfway down the "History" section and does not elaborate.

In 1937, IBM's tabulating equipment enabled organizations to process huge amounts of data. Its clients included the U.S. Government, during its first effort to maintain the employment records for 26 million people pursuant to the Social Security Act, and Hitler's Third Reich, for the tracking of Jews and other persecuted groups, largely through the German subsidiary Dehomag. The social security-related business gave an 81% increase in revenue from 1935 to 1939.

Going to the page for Dehomag, the German subsidiary of IBM, you can find the following

As an IBM subsidiary, Dehomag became the main provider of computing expertise and equipment in Nazi Germany. Dehomag gave the German government the means for two official censuses of the population after 1933 and for searching its data. It gave the Nazis a way of tracing Jews and dissidents using the powerful automated search tools using the IBM machines.

The article makes sure to clarify that "It was legal for IBM to conduct business with Germany directly until the United States entered the war in December 1941", but then at the very bottom goes on to say that IBM established a special subsidiary in occupied Poland, made the punch cards look like Dehomag punch cards, and sent the profits back to New York through Geneva.

As an addendum, this made me laugh:

Richard Bernstein, writing for The New York Times Book Review in 2001, pointed out that "many American companies did what I.B.M. did. ... What then makes I.B.M. different?" He states that Black's case in his book IBM and the Holocaust "is long and heavily documented, and yet he does not demonstrate that I.B.M. bears some unique or decisive responsibility for the evil that was done."

Way to miss the point, dude.