Some users causing 404's - garbled html?

What on earth is this?

[spagmoid]

I have PHP log all 404's on my site (with the exception of some known things, like favicon.ico, etc). Usually the report is pretty clean, but certain users on my site seem to generate loads of random 404's with nonexistent files like:

"/fg/t_%3c0.gif"
"/fg/t_msg-send.gFt.%22%3e%3cIMG%20SRC="
"/fg/t_%3c2BR%3e%3c/TD%3e%3cTD%20align=right%20ID=PadX%3e%3cIMG%20align=absbottom%20src="
"/fg.gif"

What on earth is it? It seems like their browser is actually getting garbled pages. But their USER_AGENT is pretty common. I would like to filter these people out but I don't see a way. And I assume this means they're also not seeing my site correctly. Has anyone else seen this?

[tedster]

I moved this question over here to Tracking and Logging from the Browsers forum. I don't have an answer, but I see similar things from time to time. Hoping there's an expert here.

[spagmoid]

Unfortunately I doubt this forum gets read near as much...

[Sinner_G]

Can you see the refferer page in your log? There seems to be a lot of code in there, as %something are spelled out non-ascii characters. E.g. this part

%3cIMG%20align=absbottom%20src="

would be 'translated' as

<IMG align=absbottom src="

<added>To me it looks like someone followed a badly written link.</added>

[Romeo]

... perhaps a broken UA, I have seen badly programmed private bots doing similar things ...
If it is only from a single user once a time, you probably can ignore that.

Regards,
R.

[spagmoid]

There's nothing wrong with the pages, they are shown 50,000 times a day fine... But its more than a one time thing that this happens, it seems to only be certain users, maybe one out of a thousand. I talked to a couple of them, they are newbies, not advanced enough to be using bots or spiders etc.

It seems like page data is being garbled, I would like to at least filter it out but there's no recognizable pattern to it.