I've discussed referer spam before, and its visibility in Stats logs produced by newer, less popular blogs.
There is always the odd mature and popular blog, also showing referer spam in its Stats logs. Mature and popular blogs, published by experienced blog owners, may still be subject to referer spam.
Referer spam attacks blogs of all age and popularity levels. Experienced blog owners will learn to recognise referer spam - and typically, when they identify it, they learn to ignore it.
Referer spam is less visible, in Stats logs produced by mature and popular blogs - but it is not invisible.
Most experienced blog owners can recognise most referer spam.
Most owners of mature and popular blogs learn to recognise referer spam - by observing trends between their blogs, and over periods of time. Once they recognise it, in their logs, they know to ignore it - and they move on, to more productive activity.
That is similar to how Google identifies referer spam - they can look at thousands of blogs simultaneously, and compare trends. Some trends may be visible by observing referer traffic among multiple blogs, during the same time period - and other trends may be visible by observing referer activity in one or two blogs, over a period of days or weeks.
New and subtle referer spam is not so easily recognised, by all blog owners.
With a new referer spam technique, attacking a few blogs, some owners may mistake the attack for actual reader activity.
Given a few days, the spammers will try the same technique against a different blog. Eventually, Google will identify a trend - and will remove the bogus activity, from the Stats logs on all blogs being attacked.
Activity by Google, removing Stats log entries, leads to spikes in Stats displays.
With a blog that has low genuine traffic, an owner of an attacked blog may observe the changes in pageview counts. Both the initial increase (from the attack) and the later decrease (from action by Google) may cause concern. Again, most experienced owners will ignore both changes - if even visible.
Google does care about referer spam, though they must identify it carefully.
Contradicting the impressions expressed by less experienced blog owners, Google does care about referer spam - they can simply remove spam sooner with obvious trends, than with subtle trends. They need to identify and remove referer spam carefully - because they want our Stats logs to display actual activity, when actual activity is present.
Blog owners who observe only a few samples of visitor activity, in their Stats logs, may confuse transient visitor activity, with referer spam. Again, Google, able to observe thousands of blogs, simultaneously, is better able to identify - and to remove - bogus activity from our Stats logs.
Real people do read our blogs, too. Google is simply better able to identify activity by real people - given enough time.
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