The most recent report on the number of complaints to the Telecommunications Industry Ombudsman on disputed usage charges for cable and ADSL internet for all providers nationally in the first three months of this year was 147.

The ombudsman doesn't indicate which providers were involved in these cases, but the reports to Bleeding Edge suggest that many users are not aware that they can take these complaints to there. It also suggests that network-wide, BigPond must be getting a lot of disputed bills, which BigPond denies.

A spokesman said: "A small percentage of our customers go over their monthly usage limits." He added that users "may find that occasional excess usage charges are better value for them than a higher-priced plan". While that may be true, it could also be an expensive strategy, given that BigPond's excess data charges are 15 cents a megabyte.

The reports from our readers revealed some remarkable coincidences. Like the subject of our article, two customers had also just updated their accounts when they started receiving automated emails from BigPond telling them that their free allowances were fast disappearing. Telstra says its technology staff have never heard of an instance where excess usage was triggered by a change of plan. "In fact, we have large numbers of customers who change between plans, so any such problem would clearly be apparent."

The users who wrote to us had much better security in place. They suspect that the data flows Telstra claimed to have recorded did not occur and that Telstra may be having problems with its traffic metering system. Telstra, however, says it is "confident that our usage collection and displays are correct".

One person, having had the same thing happen twice - and twice upgrading to a higher (and more expensive) limit - is particularly disturbed by the fact that Telstra has also stopped providing daily usage figures so users now can only see their traffic at the end of the month.

A Telstra spokesman said the company will introduce a new version of its software "in a month or so" to update usage "more regularly". He said customers can check account balances on the My BigPond site, where figures are updated within the hour.

What should be a major concern to BigPond customers is that at least two of the cases referred to us involved uploaded data. Most internet traffic is downloaded from websites or email inboxes, but your computer also uploads a much smaller amount, generally in the form of software requests for webpages, outgoing email and attachments. When a Trojan is at work, those uploads can reach staggering and expensive levels.

To our knowledge, BigPond is the only major internet service provider that charges for upload traffic. That means that BigPond users are the only ones exposed to unpleasant billing surprises from sources such as Trojans. In our opinion, that makes them the least attractive offering in the market.

According to the ombudsman, many users are unaware of the difference between uploads and downloads. They seem equally unaware of precisely what a megabyte or gigabyte constitutes. The SP2 patch for Windows XP, for instance, which most users would have downloaded, varied from about 80 to 265MB. Microsoft's average updates are much smaller, but they're now a regular event with an increasing number of software companies, and users on basic plans can quickly exhaust their limits.

The issue has become more critical with BigPond cutting its 500MB cable plan to 400MB last week. It now has a 400MB limit on its $39.95 monthly ADSL plan. The 500MB ADSL plan costs $69.95, but the upload and download speeds are dramatically increased, which means a month's allowance could disappear even quicker.

We recommend users check their internet traffic with DU Meter. It gives daily, weekly and monthly reports of downloads and uploads.