In general, uni-assist keeps all application documents for a year. After that they are destroyed.
Digitally collected data will be stored for a period of four years and then deleted. During this period data privacy regulations are, of course, respected: only uni-assist and the universities nominated in your application have access to the data. Your data will never be given to third parties and no statistics will be made which would allow any conclusions about individual applicants.
In general, universities delete forwarded application data after a period of up to four years. However, after you have been enrolled at a university, your data will be kept at least during the whole period of studying – in most cases even several decades.