Resignation Letter Accpeted By The Employer But Termination Letter Sent To Employee During Notice Period

I work in a small IT firm.I used to be the prime employee as told by the employer. I resigned 1 month ago and was serving my notice period.On the date of my release I did a mistake.I was copying the source codes ( not for any commercial purpose) of an application which was written by me in my personal pen drive and got caught.But I didn't take any of company's data or any thing earlier during the period of my employment.Now they are accusing me of theft and sent a termination letter.though they accepted the resignation letter with a company stamp and sent a copy of it to me over mail 1 month ago.They are threatening me to take legal actions against me and ruining my career.I don't ave any criminal record and no previous record of misconduct with this company.I don't owe any business and dont associated with any other organization except the current company.So what should I do now?what actions they can take against me? I am about to join a big mnc within one week.so how can I overcome problems of background checking and verification?how to avoid future problems regarding this?please help ASAP.

Dear friend,
It was major lapse on your part to have copied some company data on the pen drive. Generally those who are under notice period are kept under surveillance. You could have taken cognizance of this precaution that IT companies take.
Now there is only one way to come out of this predicament. It is to beg your pardon. Since you work in "small" IT company, hopefully, MD knows everybody well and so you should be. You have written that you were "prime" employee. Let us see whether your "primeness" comes handy to come out of this predicament.
Before your termination, company should have conducted domestic enquiry. Company can terminate only if your misconduct would have proved. However, at this stage what matters is your smooth exit and getting unblemished experience certificate. Therefore, you may keep aside the legal aspects of your case and concentrate on beseeching your employer.
Thanks,