Security specialist will pursue a main market listing

Security specialist Sophos is to float on the main market of the London Stock Exchange (LSE).

The firm was identified by IDC in 2007 as the largest unlisted company in the worldwide secure content and threat management market.

It is not certain how much the listing will raise, said a spokesperson for Sophos.

"It is expected that the majority, if not all, will be selldown from the existing shares of founding shareholders," she said.

Sophos was founded in Oxford in 1987 and now has 13 offices worldwide, and around 1,115 employees.

The firm has around 65,000 customers in 125 countries.

For the financial year ending March 31 2007, Sophos' billings were up 23 per cent $167m (£80m) and have grown a further 30 per cent in the first half of fiscal 2008.

Minority stakehoholder TA Associates also has a stake in Smartstream, which recently abandoned its own plans to float. TA Associates owns 20 per cent of Sophos, which it acquired in 2002 for £41m.