D&D4 Wiki

War Wizard's Expertise is an arcane class feat. It was introduced in Dragon Magazine article Tools of Two Trades, for adventurers specializing in two weapon or implement groups.[Dr402]

This expertise feat gives a +1 feat bonus to attack rolls of arcane powers and basic attacks that are made with a light blade or heavy blade. The bonus increases to +2 at 11th level and +3 at 21st level.

When using an arcane attack power with a light blade or heavy blade, attack rolls on allies take a -5 penalty.

Character optimization tends to recommend this to be used with War Wizardry, as it makes your attacks practically miss allies.  However, note that GMs may restrict using attacks that include allies - if so, consider selecting a different expertise feat.