What you guys are talking about? An offer letter is not an assurance for giving you the job. that is just an OFFER, and they mentioned that they can withdraw or cancel that offer in case of any time.
Not only UST, but every IT company is facing a crisis now. they won't take any more resources in this time, especially freshers. all these companies spoiled the industry by giving bulk salaries to the freshers, they earns not a single penny for months. So they wont take the people in this tough time because that would be a financial burden for them.
So you guys can't complain anymore, and your complaints are not legal anyway. No private sector jobs are secure especially the IT jobs. here thousands of highly skilled and experienced people are scared that they may lose their jobs in this recession, so better to find out any jobs which suits you and never ever wait for a job from any IT company in a near future. ( may be an year or so )
Many colleges wont allow the candidate to appear more than one campus placement. that is not the problem of any companies who offer a job for you. its the problem of your college. so please don't make any fuzz and understand your rights and limitations as well.