What the heck is js.users.51.la? In fact, where the heck is .la anyway? And why am I asking?
As I've mentioned before, there are possibly two gangs carrying out the current round of SQL Injection attacks, one possibly based in China and one based in Russia. Their techniques are very similar, but the seem to have distinct differences.
js.users.51.la appears in many of the "Chinese" exploits - 51.la itself appears to be a legitimate web counter site. Presumably part of the bad guys' statistical tracking system the js.users.51.la domain is combined with what appears to be a randomly named .js file.
This doesn't appear to be a malware site in itself, but it could be a useful thing to look for in your proxy logs as it may well help track down machines that have visited infected sites. Either search for js.users.51.la or perhaps just 51.la as part of your normal audit process.
Where is .la? Officially it is Laos, but the TLD is also being punted as "Los Angeles" by www.la. No clue there, but the fact that all the signups for 51.la are in Chinese really does indicate that there's a Chinese connection here.