Even if you bought 10M shares a day, you'd drive up the stock price substantially (like 2x), and now you need over a year to do it. Again it would be obvious.
When Porsche tried to be sneaky about buying VW, they started in 2004 when VW was 33 euros a share. By mid 2005 exchange rules forced them to admit what they were doing, the stock price had doubled and they hadn't even gotten to 20%. By the time they reached 40% the stock price was over 200 and actually peaked over 1,000 for a day before Porsche capitulated and was forced to sell their shares.
Thats why acquisitions are done with tender offers. The buyer may try to buy shares before the tender, but have to be careful not to break exchange rules or the law that obligates them to publicly report 1% and 5% positions when they get there.
A tender offer just says, we'll buy X% for $Y per share, and allows every shareholder to sell shares at the same price with the same info.
Since Apple's market cap is now $790B, half the value is $370B, which means that even with the cash reserves, they'd be $123B short of being able to repay, and they'd need it available on day one to execute the hostile takeover. And like they say, $100B here, $100B there, soon you're talking real money.
Essentially Apple's available cash is much less than it appears.
That's certainly one way to put it.
cool idea though
You just go to the new york stock exchange and start buying up the publicly traded stock.
In the case of Apple, it's probably a bid of near $180 a share, or $900B. Then Tim Cook goes out to institutional investors who own big chunks of stock (maybe 1% at most) and lobbies them to vote against it.
No bidder is going to be able to buy 51% of Apple in the open market in any reasonable length of time, by the time they get near 50% the price is over $400 a share.
Look at Volkswagens chart from 2005 to 2008 when Porsche was buying shares for a takeover. It started at around 33 euros, and quickly went to 70 euros after a year, eventually hitting 200 euros when Porsche got to the 40% level, and briefly spiked over 1,000 euros just before Porsche quit and was forced to dump its shares.
That is a 4-8 X return on Porsche's investment.
They came out WAY ahead. Good for them.
If price is low, then buy. If price goes into the stratosphere then sell.
Either you succeed and buy the company or you make billions on your investment.
Also they were buying on credit (leveraged buyout), which blew the whole thing up badly. And a bunch of people tried shorting it without realising the limited liquidity of VW, and got squeezed badly: http://www.reuters.com/article/us-volkswagen-idUSTRE49R3I920...