Why: If corticosteroids alone aren't working, an anti-leukotriene can block the chemicals that are further fueling airway swelling and spasms.

CNN: How to deal with your child's asthma

E-businesses using anti-fraud software now block about 8% of all transactions.

ECONOMIST: Computing

Mr Putin knows that America's proposed anti-missile system would be too small to block Russia's still powerful missile armoury.

ECONOMIST: Anti-missile defence

If Microsoft will not delay the release of Windows XP, the New York senator said he wants some of the states involved in the anti-trust case to seek a court injunction to block its release.

BBC: Privacy groups file Microsoft complaint

On October 22nd, Pfizer won a new, broad patent on Viagra, its anti-impotence drug, in America and sued Lilly to block the launch of Cialis, its longer-lasting alternative.

ECONOMIST: Despite its poor results, Lilly's future may be rosy

They tried to block the deal, but the High Court granted anti-suit orders that prevented the owners taking action in the Texas courts.

BBC: Liverpool former co-owner Tom Hicks seeks damages

Senate Democrats to whom fund managers had ties were hesitant to block the tax initiative, because it meshed with voter anti-Wall Street sentiment.

WSJ: Financiers Switch to GOP

And it could allow co-operatives like the Associated Press to reinstate anti-competitive policies that were found illegal long ago, such as allowing current members to block their direct rivals from joining.

ECONOMIST: Is the NFL more than the sum of its parts?