By Joseph Menn

SAN FRANCISCO, July 13 (Reuters) - Closely held cybersecurity firm CrowdStrike Inc has raised $100 million in a funding round led by Google Capital, giving it an undisclosed valuation that sources close to the transaction said was approaching $1 billion.

Irvine, California-based CrowdStrike had previously raised $56 million and is riding a valuation surge in both cybersecurity companies and the broader technology industry.

The company claims five of the world's 10 largest banks and three of the top 10 oil and gas firms among its clients. CrowdStrike Chief Executive Officer George Kurtz said some of the money would help expand the company's presence in Europe, Asia and the Middle East.

Google Capital partner Gene Frantz said his investment is the Google fund's first announced foray into security. It has also backed SurveyMonkey, Lending Club Corp and Glassdoor.

Other investors in CrowdStrike's Series C round include hosting provider Rackspace Hosting Inc and earlier investors Accel and Warburg Pincus.

Like larger rival Mandiant, now owned by FireEye Inc , CrowdStrike has amassed a following by researching, detecting and fighting some of the most sophisticated electronic intrusions, which are often backed by rival countries.

Such firms have gained attention and revenue as more traditional antivirus companies have come to be seen as insufficient and major breaches become a greater concern for more companies.

CrowdStrike's software reports actions being taken on endpoint user machines, whether or not they have been authorized by other programs.

Kurtz said that Google will not take a board seat but that CrowdStrike would benefit from Google advice on a range of issues, including growth and on defending mobile devices running the company's Android software.

He said that Google's deep experience with Linux will also help CrowdStrike do more to protect network-connected devices, which often run embedded versions of the open-source Linux.

(Reporting by Joseph Menn; Editing by Lisa Shumaker)