Select /Un-select multiple checkboxes in datagridview

Question

Hi There,

I have a C# application with a datagridview, this contains one column for the data value, one column for a timedate stamp and the last column is a checkbox. I need to be able to highlight (using the mouse cursor) more than one checkbox cell, then tick or un-tick all the checkboxes that are highlighted at the same time. As the datagridview may have hundreds of entries, I don't want to tick or un-tick all entires, just the checkboxes that are highlighted by the user.
I have already setup a function to tick or un-tick all entries in the datagridview
For example: If the user highlights 5 checkboxes in the datagridview, then clicks the tick in one of the checkboxes, I need this to add the tick to all 5 checkboxes that are currently highlighted, not just the checkbox that the user has clicked in, but all the checkboxes that are highlighted in the datagridview.

Please help :-)