Speed testers indicating 1.5-12 x sync speed!

[Mark v1.966]

In the last 24hrs my speed test results have gone haywire, rather than firewire, and depending on the tester, download speeds show up to 25 times the sync speed, (which remains steady at 8.186-8.187Mb/s after resetting the router [Thompson TG585v7] to check. Speedtest.net usually shows 7.9-6.9Mb/s depending on the time of day). All the online testers I've tried show massive increases, (up to 200Mb/s), with the exception of thinkbroadband.com and broadbandspeedchecker.co.uk, which are now both consistently within the normal daytime range, although the latter showed a 50% reduction in speeds yesterday. Strangely, wireless connection seems to produce even higher indicated speeds than ethernet, contrary to normal expectations, although it's hard to be sure that they are consistently higher given the amount of fluctuation.
The internet connection appears normal, pages loading at the usual speed, apart from YouTube, where videos take over a minute to load, and the broadbandspeedchecker.co.uk tester seems a bit sluggish to start and change from download to upload tests. My ISP is O2, (ADSL2+), and I'm waiting for them to get the results of a 24hr LQD test. There have been no changes to the router, or any wiring within the house, and the only software changes made in the last 24hrs have been upgrading from Kaspersky 7 to 8, and installing the latest j.r.e v1.6_10 to patch a security vulnerability. O2 have had some server problems recently, preventing access to sites outside Europe last Sunday evening, and have some throughput problems still, I gather. Can anyone suggest a probable cause of such odd test results, and are any other O2 customers having similar issues?

P.S. The distance figure shown is about 70% below what it should be too.
OS: XP MCE 2005 SP3.

[Mark v1.966]

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[Mark v1.966]

I've now discovered that the problem was caused by the Kaspersky v8 upgrade - as soon as I reverted to KIS 7 the download speeds went straight back to normal, (approximately 1Mb/s below synchronisation speed). I'm puzzled as to what part of KIS 8 was responsible as I'd tried disabling it piece by piece and it made no difference to the speed. I reinstalled it just for confirmation, and the indicated speed doubled immediately on Speedtest.net. The graph of results shows a fluctuating, (but relentless), trend towards higher and higher speeds over a period of hours, just as before. Something to do with it's application filtering training mode increasingly affecting the speed tester applets perhaps? Why on all but the two sites mentioned though? Bizarre!