Almost one in five of BT's ADSL-enabled exchanges were knocked out yesterday following a software upgrade that went wrong.

The problems started early yesterday and meant that people in those affected areas had difficulties hooking up to the service. In all, 203 exchanges up and down the country were affected with some problems continuing into the evening.

In a statement BT Wholesale said: "The problem was linked to software upgrades at 203 exchanges after which some of the units did not resynchronise correctly. Through the day and night we resynchronised the units, which meant an outage of up to an hour on each."

As of 8.30 this morning there were just 14 exchanges being re-tested before (fingers crossed) being brought back into service this morning. ®