Simple and easy to use querying tool for Oracle SQL Tools has a little drawback. Trying to remove search string from the filter, you might hit Del. This does not remove the search string but drops the table. Of course it asks confirmation. But if you accidentally dropped the table, the following command might help:

FLASHBACK TABLE table_name TO BEFORE DROP;

The latest version of the tool (1.6) has a nice feature – read-only connection to database.