No way to know whether they all will have this. I've only seen it a few times, but google searches point to ads as the primary culprit.
There's no mention of it being malicious in anything I've found. And it just seems to be an error with how the ads are coded and displayed.
No indication of any maliciousness in it either, though some websites claim its a virus and offer tools to remove it, its not really malicious in and of itself, and those websites offering removal should be ignored as well.
It's just a gif image file that some ads may use to track visits and clicks on themselves. Quite normal for ads to do.
The only abnormal thing is it being automatically downloaded, but that may just be due to some incorrect header info.
There's nothing really dangerous about it at this point.