Q: My WD hard drive might has a virus.

No anti-virus is required nor recommended. For your Trash problem see:

http://thexlab.com/faqs/trash.html

As far as I know there is no viruses for Macs. Do you have any error messages when you try to empty the trash? If you encounter issue with emptying your trash can you may find this article useful:You can't empty the Trash or move a file to the Trash - Apple Support

That doesn't convey much

What does your 'struggle' consist of?

Did you empty the trash after deleting them, before you disconnected the drive.

iKhalaf wrote:

 

i did from the first time.

but now once i disconnect my hard drive the trash is empty but re-connect my drive the files appear in the trash.

Empty the trash while the drive is connected, you can't empty the trash when it is on a disconnected drive.

There are  some junkware "cleaning" utilities that are... junk, and are known to interfere with and make it slower and harder to empty the trash, but you would never install something like that now right?

iKhalaf wrote:

 

i did not install anything that might affect my mac.

It happened with no pervious causes.

Then it's definitely not the work of any kind of malware.

What specifically happens when you empty the trash on the WD drive? Do you see any kind of error messages, or do the files appear to be deleted, but reappear when the drive is disconnected and reconnected? Have you tried repairing the hard drive using Disk Utility, and if so, what were the results?

What is the format of the external drive? If it is NTFS (a Windows format), then it is normal that you can't delete/empty the trash.