China's Lenovo Group Ltd, the world's largest PC maker, had pre-installed a virus-like software on laptops that makes the devices more vulnerable to hacking, cybersecurity experts said on Thursday. Users reported as early as last June that a program called Superfish pre-installed by Lenovo on consumer laptops was 'adware', or software that automatically displays adverts. Robert Graham, CEO of U.S.-based security research firm Errata Security, said Superfish was malicious software that hijacks and throws open encrypted connections, paving the way for hackers to also commandeer these connections and eavesdrop, in what is known as a man-in-the-middle attack. Lenovo had installed Superfish on consumer computers running Microsoft Corp's Windows, he added. "This hurts (Lenovo's) reputation," Graham told Reuters. "It demonstrates the deep flaw that the company neither knows nor cares what it bundles on their laptops." An administrator on Lenovo's official web forum said on Jan. 23 that Superfish has been temporarily removed from consumer computers. Lenovo executives were not immediately available for comment during the Lunar New Year holiday in China.