this article explains in depth what the problem is. the SEC has now been alerted to the problem, and is investigating. the people who found the issue believed originally that this was deliberate, but it actually just turned out to be a systemic problem of the speed differentials between different routes that high-frequency trades come in at.
what they originally discovered was that they could see a price on a screen, but the moment that they put in the bid to a number of brokers, the price would DISAPPEAR. they thought that this was deliberate, that someone was scamming them: it turned out that this wasn't true, but it took a couple of years of investigation to find out. what they did was they put in *individual* bids *directly*, and found that they were accepted. they then investigated various combinations, introducing delays into the bids, and found, amazingly, that it was down to the *time of arrival at the exchange* of their bids as they were sent via numerous brokers.
so it was only when they invented a tool (which they called "Troy") that *deliberately* introduced networking delays, such that the bids would (as best they could manage) arrive within milliseconds of each other at the exchange, that they managed to trade successfully.
if however any one of those bids happened to go via a different ISP, or a different router, or any other random combination, then the bids would *FAIL*.
the problem it turns out is that these delay effects are well-known. most of the money in high-frequency trading is therefore made by seeing a slightly slower broker's prices, then putting in an undercutting bid *knowing full well* that the other broker has a slower network. and this aspect of high-frequency trading is what is currently under investigation by the SEC.
*this is why the introduction of networking delays is so absolutely important*.
the people who discovered this phenomenon basically had to set up their own independent exchange in order to solve the problem. they needed to introduce a delay of 350ms as a way to make things fair for everyone. they did this by basically putting in 38 miles of fibre-optic cable in a shoe-box in the basement of the server farm that they leased.
it turns out that once investors discovered this, they began *specifically demanding* that their trades *exclusively* be brokered through this new exchange that had this 350ms shoe-box delay. it actually caused a lot of embarrassment for a number of brokers and trading houses because the brokers were explicitly disobeying their client's instructions, because the brokers didn't understand how important this really is.
anyway: you really have to read that article (or the book) fully because it's quite complex, and it's basically an inherent flaw down to the fact that the internet (TCP/IP) is routed randomly, thus introducing gross unfairness that has become the subject of intense investigation, very recently.
so yes, *all* trading should be done with at least a 350ms delay.