Tax on us income

I worked in US from Feb/26/2006 to Jun/16/2006 for approx 3.5 months. I paid taxes in US for the income earned during this period. The US income earned was transferred to my India regular Savings A/c after returning back. While filing my tax returns in India for the Year 2006-07, I did not report the US income. I had only reported the Indian income earned from June-2006 to Mar-2007. Recently, I received a email letter from income tax requesting to pay taxes on this income. Requesting your guidance:
- Is this income taxable in India?
- What is the process to clear this issue with the income tax department?

Regards
Vijay