By Nikhila Natarajan New York, July 30 : Four big tech CEOs -- Facebook's Mark Zuckerberg, Amazon's Jeff Bezos, Sundar Pichai of Google and Tim Cook of Apple -- pushed back against accusations during a US Congress panel hearing capping a yearlong investigation into these companies' market domination online. Amid intense grilling on issues that centred on market power derived from uninhibited collection and access to data, all four CEOs focused their attention on the value of their innovations and services to consumers. They testified via video link to lawmakers in Washington, DC. Google CEO Sundar Pichai struggled to deflect accusations of anti-conservative bias and retreated multiple times to a "Happy to engage with you" answer in response to questions that went deep into the working of the company's mighty algorithms. Pichai squirmed when asked whether he signed off on the company's 2016 decision to merge data from the advertising company Double Click -- bought in 2007 -- with Google's own data. Rep. Val Demings described this move as one that effectively "destroyed users' anonymity" on the internet. "I reviewed at a high level all the important decisions we make," Pichai said. He talked up how Google "cares" about privacy and security of users and noted that Google no longer uses data from Gmail for ad targeting, a relatively recent change. Amazon CEO Jeff Bezos repeatedly offered "I don't remember" or "We are looking into it" as an answer to lawmaker concerns about how the company might be killing off small businesses, poaching ideas from competitors or employee testimony that there is "nobody enforcing" policies in a company that has become a "candy shop" of seller data. For years, Amazon has been dogged by allegations that it uses its dominance to identify and enter into new product categories using its unique lens into inside information on third party seller data. Pushed on this question by Pramila Jayapal, who represents the district in which Amazon is headquartered, Bezos sidestepped saying he could not answer yes or no. "I can tell you we have a policy against using seller-specific data to aid our private label business but I can't guarantee you that that policy has never been violated." Facebook CEO Zuckerberg faced fire over the company's acquisition of Instagram and WhatsApp, a pervasive strategy of copying competitors' features, selling user data to third parties and the forest fire analogy of how fake news and conspiracy theories go wild on the mighty platform. In his responses, Zuckerberg admitted that Facebook has "certainly adapted features that others have led in" but countered that the company's moves were not anti-competitive. "I have always been clear that we viewed Instagram as both a competitor and as a complement to our services," Zuckerberg said. The Facebook's CEO used his time during opening remarks to knock competitors. "In many areas, we are behind our competitors," he said. "The most popular messaging service in the US is iMessage. The fastest growing app is TikTok. The most popular app for video is YouTube. The fastest growing ads platform is Amazon. The largest ads platform is Google." "Apple CEO Tim Cook contended that his company does not have a dominant market share "in any market where we do business" and prioritises the quality of product versus scale. Apple, whose iPhone is the world's third-largest selling phone, is facing EU investigations over fees charged by its App Store and technical blockades that allegedly shut out competitors to Apple Pay. Cook said, "In the more than a decade since the App Store debuted, we have never raised the commission or added a single fee. In fact, we have reduced them for subscriptions and exempted additional categories of apps. The App Store evolves with the times, and every change we have made has been in the direction of providing a better experience for our users and a compelling business opportunity for developers." /IANS