I think that it would be SQL injection if you enter data like this . Data coming from user input should always be checked and before sending to the database.
Using ASP.NET you need to remove all HTML tags from the post back because the framework checks for possible HTML injection coming from the user input .
After removing the tags (or replacing the < by something like < and necessary symbols also ) and converting back in the server when viewing data.
You can use the the HtmlEncode() and HtmlDecode() methods to convert the data before saving and retrieving data .
Refer posts it may help you
How to save HTML content in database
http://forums.asp.net/t/1441293.aspx