By their actions!
United States Patent Application: 0070033102
A patent granted to Microsoft for a technology which forces computer users to watch ads, with "sanctions" if they don't ....
" ...The policy may be directed to a single computer and thereby a single user or subscriber. Alternately, the policy may extend to a group of computers and correspondingly to a common owner, for example, a business or school. When the limit of incorrect responses is reached as an aggregate of group of computers, a sanction may be imposed or a higher level of monitoring may be initiated.
 The user's actions following the verified advertising delivery may be monitored. "