BT has bought an anti-hacking company which protects the computer systems of some of the world's biggest companies.
Counterpane is "a leader" in computer network security, BT says.
California-based Counterpane Internet Security monitors about 550 networks for a host of global businesses.
Its founder, Bruce Schneier, is widely acclaimed in the industry and was mentioned in the Da Vinci Code as one of the world's leading cryptographers.
BT paid an undisclosed sum for the firm, which had assets of $6.8m (£3.6m) at the end of 2004.
The purchase was welcomed by the chief executive of BT Global Services, Andy Green.
"As more and more of our customers seek to exploit the opportunities of globalisation, we are finding that, increasingly, business critical applications are dependent upon the resilience and security of their infrastructure," he said.
"As security threats get more sophisticated, a larger number of companies are outsourcing the management of their security infrastructure to specialised security service providers and Counterpane is a leader in this space".
Mr Schneier will remain as chief technology officer at Counterpane and Paul Stich will stay on as chief executive.