I booted from the Ubuntu ISO which I burned on a disk and installed Ubuntu, and chose the option to replace windows 7 with Ubuntu, now the version of windows 7 I was running was an illegal cracked version and I already had tried to get rid of it without booting into the actual OS and after many attempts was unsuccessful. Now did installing Ubuntu and choosing the option of replacing windows 7 actually solve my problem and did it wipe the previous windows OS EVERY LITTLE PART OF IT.
If you choose to replace Windows then the hard drive is re-partitioned and formatted completely. You can be fairly sure that Windows no longer exists.
You can verify this by opening a terminal windows and typing
which will show all drives and all partitions on the system. You should find that there are absolutely no NTFS Windows partitions on the machine. If there is a second hard drive in the machine, and if Windows was installed on that also, then it's possible that it might still exist.
Your Data Might Still Be Recoverable (But Don't Count On It!)
Since, as you commented, your goal is to ensure that no data from the Windows system can ever be recovered:
No. Nothing you could have done with the Ubuntu installer utility can completely eradicate all possible informational trace of previous data on your disk.
You can, however, probably accomplish this, and if you wish, you can probably accomplish this with the Ubuntu live CD. (You cannot accomplish it from within a running operating system installed on the drive, like your newly installed Ubuntu system.)
To render all data on a disk permanently unrecoverable, you need to overwrite every byte on the disk. This takes a moderately long time (up to several hours, or days for disks that are really big and also really slow).
According to some respected computer engineers and data recovery specialists, to be entirely sure you're destroying all the data, you have to overwrite it with unpredictably random bytes. (On the other hand, my understanding is that some equally learned folks think that's not necessary.)
If you're really interested in doing this, see:
But is that really what's important?
The potential recoverability of data from your old Windows system is entirely irrelevant to all of the following:
Futhermore, assuming the Ubuntu installation worked properly (which is something we can check, see below), you will not be accidentally booting into the old operating system. To get it to even start booting you'd probably have to try hard. If you got it to boot all the way, that would be truly impressive.
Sometimes You Really Do Have to Destroy All the Data Completely
If there is information in your old Windows system that must be kept secret, for example if you are ethically or legally obligated to ensure that it is not disclosed, then it is a good idea to scramble the disk completely (as discussed in the two questions linked above).
If there is information in your old Windows system that is so sensitive that one or more people could plausibly die as a result of its disclosure, or that something comparably bad could result, then you should scramble the disk completely. Then, you should physically destroy the disk. The reason for this is that, even if the likelihood is small, it is possible that you could make a mistake (or that your software tools could have a bug) that would cause some data to survive. I am not familiar with what techniques are recommended for physically destroying hard disks, but some government agencies and some businesses do actually have protocols for that sort of thing, some of which can be read by interested members of the public.
I am guessing your situation is not like either of those two. This section is included for completeness only (and in case you were wondering under what circumstances I recommend making sure all data on a disk are completely destroyed).
Peace of Mind Is An Acceptable Reason to Securely Erase a Disk
It takes a bit of time to read and absorb information about secure erasure techniques. But deciding what technique or utility to use is ultimately not too difficult, and most hard drives these days don't take overwhelmingly long to overwrite.
Therefore, if it makes you feel better to do it, do it!
Of course, this will overwrite your new Ubuntu system, too. But you just installed it, so you probably haven't customized it much yet. You could probably reinstall it without too much hassle.
It is almost certainly not necessary for you to securely erase your disk, but it's kinda cool, so if you feel like it, go ahead!
You Should Check Your Partition Table(s) to Make Sure Ubuntu Installed the Way You Wanted
Without checking your partition table, you don't know for sure if the Windows partitions themselves were really wiped out. If they weren't wiped out, your Windows system might be fully accessible and you might even end up booting to it again (though this is still not extremely likely, assuming it's not booting now and there's no menu option for it).
It's a good idea to do this. Here's how:
I believe checking your partition table to make sure there are no Windows partitions left over is quite sufficient, and I think most other experienced users would agree. Please do not hesitate to ask if you want help interpreting the output of