Apple this week became only the second company ever to be worth more than $600bn (€457bn) -- albeit briefly.
With Apple stock changing hands at $644 per share, the company's market capitalisation flirted with the mythical barrier on Tuesday, temporarily breaching it before falling back later in the day.
By yesterday morning in the United States, the stock was trading at $632, giving it a market value of just under $590m.
It had been worth $500bn at the end of February.
Microsoft is the only other company to have ever seen its market value top $600bn. It was worth $619bn at the end of 1999 -- the height of the dotcom boom.
Yesterday the US Justice Department filed a price-fixing anti-trust lawsuit against Apple over the pricing of eBooks. Other publishers, including Penguin, HarperCollins and Macmillan, were also sued in the same case.
Apple and Macmillan, which have refused to engage in settlement talks with the department, deny they colluded to raise prices for digital books.
They will argue that pricing agreements between Apple and publishers enhanced competition in the e-book industry, which was dominated by Amazon.
The department is probing how Apple changed the way publishers charged for e-books on the iPad.
Gina Talamona, spokeswoman for the US Justice Department's anti-trust division, and representatives of Apple, Simon & Schuster, Hachette and Macmillan, which is a unit of Verlagsgruppe Georg von Holtzbrinck, declined to comment on prospects for lawsuits or settlements. Additional reporting (Bloomberg)