Microsoft has urged businesses running Windows XP to upgrade their machines to take advantage of added security features, but only a quarter of XP corporate machines have been upgraded to Service Pack 2, according to a new study.

In a study of 136,000 corporate PCs, Canadian asset tracking firm AssetMetrix found that more than one-third of the computers were running Windows XP, but only 24 percent had installed the security-oriented Service Pack 2 upgrade. Companies were initially reticent to jump to SP2 when it debuted last year, but the AssetMetrix study found that most companies weren't blocking SP2 entirely; they just had not upgraded in large numbers. Of the 207 companies that were using XP on at least 10 machines, about 40 percent were blocking SP2 universally. At the other extreme, about 8 percent had forced the SP2 on all XP-based machines as a matter of policy. "Very few companies have drawn the line in the sand," said Steve O'Halloran, managing director of AssetMetrix Research Labs. "A good deal of the companies have a mixed environment."