Alphabet Inc's Google is buying cybersecurity firm Mandiant Inc for $5.4 billion, adding heft as rivals Microsoft and Amazon also look to beef up security for their fast-growing cloud units.

The deal will enhance Google's cloud computing business, which generates more than $19 billion annually, and bolster its security operations and advisory services, the company said on Tuesday.

The Information reported the news first on Monday.

Microsoft Corp was also said to be eyeing a buyout of Mandiant, according to news reports. The software giant had previously forecast spending $20 billion spend on cybersecurity over the next five years.

Google's offer of $23 per share represents a premium of about 53% to Mandiant's stock price levels before reports that Microsoft was eyeing a deal.

Shares of Mandiant fell 2%, while those of Alphabet rose 0.2% to $2532.20 in premarket trading on Tuesday.

Mandiant, which focuses on cyber-incident response and cybersecurity testing, became a standalone entity last year when FireEye Inc, which acquired the company in 2013, sold its products business and the FireEye name for $1.2 billion to a consortium led by private equity firm Symphony Technology Group.

The firm has become a go-to for news organizations and companies for investigating cyberattacks, including recent breaches at News Corp and Nvidia Corp.

The deal is expected to close later this year.

(Reporting by Eva Mathews and Nivedita Balu in Bengaluru; Editing by Vinay Dwivedi and Saumyadeb Chakrabarty)