Users of a popular accounting package have been warned not to use the software at public Wi-Fi hot spots, such as those found in coffee shops, airports and hotels.
Users of the 2006 Mac version of Intuit's QuickBooks software could find that a serious bug manifests itself again under certain conditions in Wi-Fi hot spots.
QuickBooks is one of three key product lines for Intuit, whose software has been sold to thousands of small businesses across the world.
The bug, which was contained in a flawed product update released in December, has already been responsible for deleting documents, including financial files, from users' PCs.
QuickBooks released a patch for the bug on Saturday, but warned users two days later of the dangers of using the QuickBooks software when connected to Wi-Fi hot spots.
"We have determined that the prior bug remanifests itself when QuickBooks Pro 2006 for Mac is initiated at public Internet hotspots and a redirection error occurs (for instance, when you are at a cafe that requires you to pay to use its services)," wrote Ian Vacin, leader for Mac financial software at Intuit, on the company's Web site.
"If you must use QuickBooks Pro 2006 for Mac at Internet hot spots over the next few days, please contact us directly... so that we can provide you a temporary work-around."
Vacin said that Intuit would release a patch in the "next few days" that will disable the software's upgrade mechanism and so cure the issue.
Intuit also urged users to download Saturday's patch because if they don't a refresh of the users' preferences could result in the original bug occurring again.
Although the company is releasing patches to address the problem, it has so far been unable to recover lost data from users' machines.
Data-recovery companies can often recover deleted Mac data, as long as the files have not yet been overwritten.