Web threats are malicious programs that is lurking on the Internet. These threats varies depending on the type of attack that they do. Can you tell us more what seems to be happening on your computer when you notice that you "have" web threat on your computer?
Common scenarios are the Technical Support Scam: This threat will create a pop on your screen saying that there is an infection on your computer and that your files are in danger and you will need to contact the number that they are providing in order to resolve this issue.
This scam is dangerous as they will attempt to control your computer remotely and will have the ability to cause more damage on your computer or collect private files without you having the knowledge about it.
You can learn more about this by clicking on this link.