When playing internet Blackjack let's assume that the dealer has an Ace up, and you decide to take insurance for the full amount, or $5. Now, two things can happen:

    1) The dealer has a Blackjack. I tie with the $10, but collect 2:1 on the $5 insurance bet for a total profit of $10.

    2) The dealer does not have Blackjack. I lose the $5, but collect $15 for my BJ. Total profit, again $10.

So, casinos allow me to eliminate the insurance bet all together, and simply declare that I want even money for my blackjack when the dealer has an Ace showing.

You're probably thinking that sounds like a pretty good deal. You're guaranteed a profit even if the dealer does have Blackjack. Just remember that the guaranteed profit comes at a price. You'll win more money in the long run by holding out for the $15, even though you'll sometimes end up empty-handed. Nonetheless, many players are adamant that they prefer to take even money when offered. Just be aware that you're costing yourself money when you make that choice.

The basic strategy player should simply never take the insurance bet, even the "even money" variety. Card counters on the other hand can often detect situations where more than one-third of the remaining cards are ten-valued, and the bet is then a profitable one. So, unless you know the bet is favorable, just ignore it.