Yahoo! Inc., owner of the largest U.S. Web portal, jumped as much as 7.1 percent in Nasdaq trading on a report that KKR & Co. is joining a list of buyout firms that want to take the company private.

KKR is interested in helping finance a transaction, the New York Post reported today, citing unidentified people. Private- equity investors approached Alibaba Group Holding Ltd., which is 40 percent owned by Yahoo, about taking Yahoo private, Reuters reported, also citing people familiar with the matter.

Yahoo had lost half its value since Microsoft Corp., the world’s largest software maker, withdrew a $44.6 billion bid in 2008, and sales haven’t grown much under Chief Executive Officer Carol Bartz amid competition with Google Inc. Goldman Sachs Group Inc. is working with Yahoo to help defend against takeover approaches, people with knowledge of the situation said last month.

Yahoo climbed 96 cents, or 5.8 percent, to $17.40 at 10:58 a.m. New York time on the Nasdaq Stock Market, after rising to $17.60 in the biggest increase in almost four weeks. The shares had declined 2 percent this year before today.

Kristi Huller, a spokeswoman for KKR, declined to comment, as did Alibaba spokesman John Spelich. Dana Lengkeek, a spokeswoman for Yahoo, didn’t immediately return a phone message seeking comment.