IITs aim to churn out future leaders of society. So IIT life would try to equip its students with as much diversity and opportunities as possible. So within IITs you have all kinds of events. There are three fests in each academic year - one cultural fest, one technical fest and one sports fest. Additionally there are clubs for things like dramatics, music, arts, indoor sports etc etc which are about 10-15. Also you have most of the sports in IITs. Now to keep the system running IITs hold different positions to run these clubs and various activities both academic as well as non-academic. For every activity there's a student secretary and there are numerous representatives which help making the process a success. Naturally for each activity, club or any event there's a budget which is decided and bills are submitted during due course fitting that budget. Be it fudging of bills, be it use of budgets for personal benefits etc etc everything is done by the students. There's a whole host of politics involved in the selection of secretaries and reps. The funds of these events are also used for lavish treats. Some part of it is right, some not. People can differ on that.
To get a sense of money a student secy can make is that at the end of a fest, people are able to their dream bikes financed. Mess secretary is a very coveted post as it involves managing the budget for a hostel's mess and can get you in a good position to exploit the tricks of trade. On the other hand sometimes bills do not get cleared easily for representatives. The secy's who head them have better ways to use them. Everybody know what are those. The big cut is obtained when you set up something big. So say a pool table for your hostel or renovation of the hostel garden. Everybody takes a cut for taking a initiative but how much is the question. But these are small if you consider their impact and if there was a way to quantify the wrongdoing all these are not so severe.
One big thing that happens from the end of students which I have witnessed is the scholarship from the institute which waivers tuition fees of students coming from family below a certain annual income (about 2-3 lakhs). There were about 15 people atleast (out of 50 in our batch) that I know in my hostel in my year who fulfilled the criteria on paper just because there was no proof to ascertain their family income. I am not sure about how many more did the same. Anyways the percentage was huge I can tell you that but still the authorities at IIT did nothing about it. The scholarship is like 30k for tuition fees and another 18k for the year. So its roughly 50k per student that IIT spends per year which it should save. Anyways that is the way it is.
One more shady area which I cannot confirm by examples but know happens in from the end of professors. When you get those equipments in laboratories, they misrepresent the prices and inflate bills to the tune of many lakhs for personal benefits. Also the institute infrastructure is a big money churning area for the people in charge. A friend of mine in IIT Roorkee told me a certain road was build over and over just to because it offered good margins for takers. This and many more happens in our premier institutes and our future leaders are part of it. No wonder a stalwart like Rajat Gupta is under scrutiny. But that's the way it is.