@gta0gagan,i said nothing incorrect.you do need correct encryption key to decrypt data even if it involves brute forcing using various tools.
@harshilsharma63,i just encrypted a 54mb avi file using winrar which uses AES encryption & it took just 22 sec & ~89% cpu usage on my pentium G620 system.on a quad core/core i system this will take even less not to mention documents like pdf,office documents etc are smaller in size & malware probably encrypted most of these files during idle time when system was on but user was not there(indicated by very low cpu usage) or doing something which would hardly use 3-4% cpu leaving rest for encryption.
@harshilsharma63,i just encrypted a 54mb avi file using winrar which uses AES encryption & it took just 22 sec & ~89% cpu usage on my pentium G620 system.on a quad core/core i system this will take even less not to mention documents like pdf,office documents etc are smaller in size & malware probably encrypted most of these files during idle time when system was on but user was not there(indicated by very low cpu usage) or doing something which would hardly use 3-4% cpu leaving rest for encryption.