By Foo Yun Chee and Eric Auchard
BRUSSELS/FRANKFURT (Reuters) - Beyond a headline-grabbing 2.4 billion euro ($2.7 billion) fine EU antitrust regulators have levelled against Google, the internet giant is likely to be shackled for years by Tuesday's precedent-setting decision defining the company as a monopoly.
The ruling opens the door for further regulatory actions against more crucial parts of Google's business – mobile phones, online ad buying and specialised search categories like travel - while easing the standard of proof for rivals to mount civil lawsuits showing Google has harmed them.
So far, investors have shrugged off the EU's threatened crackdown, with Google's holding company Alphabet's shares down 1.8 percent in early U.S. trade amid a continued selloff in technology stocks.
The stock has doubled in the two years since European authorities vigorously stepped up investigations of it.
It trades just behind rival Apple as the world's most valuable stock with a $666 billion market capitalisation.
The real sting is not from the fine for anti-competitive practices in shopping search but the way the EU has thrown the issue back to Google to solve, meaning the company won't be able to comply through an easy set of technical steps.
In effect, the Commission is forcing Google to demonstrate that rivals have made substantial inroads into its businesses before there is much chance of it being let off the regulatory hook.
EU competition chief Margrethe Vestager promised Google was in for years of monitoring to guard against further abuses.
"Just being put on notice can limit Google's strategic options into the future," said Matti Littunen, a digital media and online advertising analyst with Enders Analysis in London.
The EU's 2004 ruling that Microsoft Corp had abused its dominant market position in Windows and other markets is now seen as having curtailed the software giants moves over the subsequent decade to expand more quickly into emerging markets such as online advertising, opening the way for Google's rise.
Putting the onus on the company underlines regulators' limited knowledge of modern technologies and their complexity, said Fordham Law School Professor Mark Patterson.
"The decision shows the difficulty of regulating algorithm-based internet firms," he said. "Antitrust remedies usually direct firms that have violated antitrust laws to stop certain behaviour or, less often, to implement particular fixes.
"This decision just tells Google to apply 'equal treatment,' not how to do that".
The EU ruling is a warning shot for two on-going EU probes into Google's Android mobile operating system and AdSense ad system, said Richard Windsor, an independent financial analyst who tracks competition among the biggest U.S. and Asian internet and mobile players, including Google.
"If the European Union turns around and says Google can no longer bundle its Google Play app store as a default feature on many Android smartphones, this opens up the market to other handset makers to put their own software and services front and centre on their phones," he said.
Littunen of Enders Analysis agreed, saying while Google may be able to meet EU objections in the AdSense case by making relatively modest changes to its advertising systems to enable website customers to run ads from Google advertising rivals, the Android case has many complicated factors with no easy solution.
More importantly, Google must find ways change its business practices without harming its very lucrative advertising business model, which accounted for around 85 percent of the $90.3 billion in revenue of parent company Alphabet in 2016.
"The EU's identification of 'super-dominance' in internet search throughout the European Economic Area is confirmed and will provide a cornerstone for assessment of other ongoing cases, especially regarding Android and AdSense," said Jonas Koponen, competition chief at Linklaters law firm in Brussels.
"This could result in a profound change to the company's business models," he predicted.
Yet another worry for the company could be a wave of lawsuits in the future.
"We can expect to see a series of damages claims brought by the rivals that were excluded from the market by Google's conduct," said Peter Wills, co-head of competition law for Bird & Bird in London, setting the stage for national court battles.
With the EU's Vestager giving no ground in her record demand last year to collect 13 billion euros in unpaid taxes from Apple and stopping Google from squeezing out rivals, other tech giants will probably think twice before testing her further.
($1 = 0.8862 euros)
(Editing by David Evans)