Google has launched a new portal you can use to personalize the ads you see, and it has begun notifying users about it through either Chrome or Gmail. You can add topics of interest and your age and gender to see advertisements the cater to you on Search, YouTube and other Google services. But if you don't want to share those info with the big G, you don't have to -- the feature is completely opt in. If you agree to switch it on, you're also giving the company permission to use your Google account activity on its services. That includes giving it permission to keep track of what ads you interact with and to add that info to its new My Activity site.