Warren Buffett said his Berkshire Hathaway Inc. has invested $10.7 billion in International Business Machines Corp. this year, a major shift for a billionaire investor who has famously avoided technology stocks.

Berkshire purchased about 64 million shares, beginning in March and building the stake throughout the year, Mr. Buffett said in an interview Monday on CNBC business television. Mr. Buffett's purchases appear to make Berkshire one of IBM's two largest shareholders, with a stake of roughly 5.4%, and come as IBM's stock has repeatedly set all-time highs.

IBM shares rose 0.9% to $189 in morning trading, valuing Mr. Buffett's holdings at about $12.1 billion. That would make IBM the second-largest equityholding in Berkshire's stock portfolio, behind only a $13.6 billion position in Coca-Cola Co., according to FactSet.

The new stake in IBM marks a change for Buffett, who has famously eschewed tech stocks despite a long friendship with Microsoft Corp. co-founder Bill Gates, a member of Berkshire's board. Mr. Buffett said he had gained added insight on IBM in reviewing the company's regulatory filings, and said he had been 'hit between the eyes' by the advantages the company enjoys in finding and keeping clients.

In addition, he had discussed the company with the information-technology departments at several of Berkshire's subsidiary companies, and drawn upon his own expertise from decades ago, when he had tried to market competing technology to companies, only to be told that 'no one had ever gotten fired' for selecting IBM as their supplier.

'It's a company that helps IT departments do their job better,' Mr. Buffett said. 'It is a big deal for a big company to change auditors, change law firms,' or for IT departments to move away from using IBM, he said. 'There is a lot of continuity to it.