Sometimes people simply do not realize they are indirectly hurting the system by voting for a user rather than rewarding good content. You can simply explain this to them. They should also know that they can actually be hurting the user when the system detects this activity and their well-meaning votes are removed in bulk.
The system has processes in place to detect various types of targeted voting between users and groups of users. But if you suspect a user is disproportionately voting for a user rather than voting broadly for good posts, please feel free to pass on an appropriate excerpt from the guidance they will receive if they get caught up in this activity.
We recently noticed a substantial number of votes on your account to or from specific users. Please note that votes on Ask Ubuntu should be cast to reflect the quality, accuracy, and relevance of the posts being voted on.
While we encourage everyone to up-vote great posts, the motivation for doing so needs to be anchored in the merits of the post, not the person that wrote it. Please refrain from targeting specific users' posts when voting. Stack Exchange strives to ensure that everyone who has a question sees the best information first; intentionally voting for content simply for the benefit of your family, friends or co-workers unfairly skews that system, and can result in a lengthy timed suspension for all concerned.
The offending votes have been invalidated. In the future, please ask people that you know to refrain from voting for your contributions simply because you wrote them. Additionally, please don't engage in this behavior yourself.
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