I've noticed since the recent update to McAfee® Internet Security 15.1 R2, in Virus and Spyware Protection -> Real-Time Scanning, the 'Options' pane has disappeared. All that's there now is 'Excluded Files'. Options before allowed you to modify real-time scanning (such as scanning for viruses using threat patterns, scanning removable drives, scanning for spyware. etc) and now none of these choices are available.
I've also noticed in 'Scan Your PC', the option of a custom scan has disappeared (now only available in the context menu).
I'm very disappointed with the cancellation of this option. I've been using McAfee for many years.I hope you will consider adding this read-write scanning option in future versions. The current version of real-time protection only supports "write scanning", which is very necessary. In addition, this option is available in other versions of McAfee, which can enrich customers' choices and let them decide what form of real-time protection to use.