IDC rates Fortinet as securing around 15% of the UTM marketplace and, according to the IT security vendor, it expects to issue around 5.8 million shares.

Fortinet backers also plan to offer a further 6.7 million shares, up from a previously announced 6.2 million, according to a filing with the Securities and Exchange Commission.

The company, which is based in Sunnyvale, California, said its revenue increased from $38.7m in 2004 to $211.8m in 2008.

Infosecurity notes that the IPO's underwriters, Deutsche Bank, JP Morgan and Morgan Stanley have the option to buy up to 1.9 million additional shares to cover overallotments.

On the first day of trading - Wednesday - Fortinet's share price soared by around 30% in the first full day of trading, prompting Bob McCooey, vice president of NASDAQ to say: "this is what investors have been waiting for" to reporters.

McCooey told financial journalists that between 25 to 50 Silicon Valley technology firms in the last six weeks have begun selecting banks to help take them public.

The Fortinet share price ended the day at $16.62, up from the initial price of $12.50 per share. The offering raised $156.2 million for the company, with net proceeds expected to be $66.2 million after expenses, Fortinet said in its filing.

Incorporated back in 2000, Fortinet is backed by Acorn Campus Ventures of Cupertino and Redpoint Ventures of Menlo Park, California.