By Emma Rumney and Eric Auchard
LONDON (Reuters) - Avast, the world's largest consumer antivirus supplier by customers, said on Thursday it will apply to list its shares on the London Stock Exchange in what could be a blockbuster float expected to value the company at around $4 billion.
The listing, which is anticipated in early May, will see a free float of at least 25 percent of Avast's issued share capital with the aim of raising around $200 million in primary proceeds.
A source familiar with the matter said the firm also hopes to raise a further $800 million via secondary sales, meaning an overall target of around $1 billion and bringing the firm's valuation to $4 billion if successful.
That would represent the largest ever UK technology IPO and puts it head to head with British competitor Sophos, the only other cyber security firm listed in London.
It will be Avast's second attempt at an IPO after it scrapped a plan to list on the U.S. Nasdaq in 2012 due to tough market conditions.
Founded three decades ago in the former Czechoslovakia in the waning years of Communism, Avast claims to provide basic antivirus defenses to 40 percent of consumer PCs outside China, where foreign security products are banned.
It has grown amid a dramatic increase in the number and type of threats since it was founded in 1991, and thanks to its ability to "stay ahead of the bad guys", CEO Vincent Steckler said.
"A listing on the London Stock Exchange is a natural fit, providing us wider access to capital markets and supporting the future growth of our business in the years ahead," he said in a statement.
Avast will also use the primary proceeds of the offering to pay down its debt, its statement said.
The company was a pioneer of the now widely used 'freemium' business model, distributing its antivirus products for free over the internet, then charging customers for premium features.
It counted 435 million users at the end of last year, including 290 million consumer PC users and 145 million mobile users, and a turnover of $780 million. It acquired AVG, a Czech rival, two years ago to significantly expand its user base.
As well as antivirus software, it also supplies privacy protection and other internet utility software, targeting both consumers and small- and medium-sized businesses.
In a fragmented market, Avast competes with brands including Czech-based ESET, Malwarebytes and McAfee, both of Silicon Valley, Romania's Bitdefender, Britain's Sophos and Kaspersky Lab of Russia.
Avast's public offer follows the successful listing of two other high profile "freemium" companies in the United States.
Dropbox, which started as a free service to share and store photos, went public last month and music-streaming Spotify had the largest ever direct listing earlier in April.
Morgan Stanley and UBS have been appointed joint global co-ordinators and lead bookrunners for Avast's IPO.
It is 46 percent owned by its founders, Czech entrepreneurs Pavel Baudiš and Eduard Kučera. CVC Capital Partners has a 29 percent stake, with Summit Partners holding 7 percent.
(Reporting by Emma Rumney and Eric Auchard, additional reporting by Paul Sandle, editing by Silvia Aloisi/Sinead Cruise/Susan Fenton)