I've been using an external hard drive in Windows, but now that I decided to switch to Ubuntu, I wonder if I can safely remove the folders
Feel free to delete all the folders you mentioned. Ubuntu does not use them, and instead uses its own recycle folder called ./Trash
Edit 1: Expect Microsoft Windows to re-create the recycler-related folders the next time you connect the drive to a windows machine.
Also, the found.000 folder indicates your hard drive had a problem reading data in the past, which Microsoft scandisk caught and tried to recover. If the data on the drive is important to you, please ensure you have a current backup of that drive.
Thanks to brunopereira81 for mentioning the source of the found.000 folder.
Hope that helps
Yes, unless you use your recycle bin as a quick archive for your files (had a friend that did that... "I press delete and all my files are quickly saved under the same place, find a program that does the same and I will stop using the recycle as my archive!") ;)
The 2 first ones are recycle bin related, AVG probably is your quarantine folder for AVG and found.000 is a trace from a scandisk you ran.
If you are not planning to use windows again it is safe to delete those folders.