About 90 percent of the 165,000 Web sites hosted by NaviSite that had been down since Saturday are back online, the company said Thursday. The sites were offline because of a failed datacenter migration involving the Andover, Mass.-based Web hosting company.

The problems occurred when NaviSite attempted to migrate and replace hundreds of servers operated by Baltimore-based Alabanza , a Web hosting company that NaviSite acquired in August.

According to NaviSite spokesman Rathin Sinha, the remaining sites should be back online later this evening. "Things are going as planned," Sinha said.

However, some NaviSite clients are threatening to find other Web hosting companies once they are back online and have retrieved all their files. Others are threatening class-action lawsuits. The law firm of Wolf Popper LLP in New York confirmed that it had been contacted by NaviSite clients and was looking into the issue.

Joseph Blaney, CEO of Global School Sports, which yesterday announced it had selected the NaviSite Online Video Publishing Platform to deliver its content to its customers, said his company was in the process of working with NaviSite to get through this "mishap" and move forward.

"While it doesn't affect us directly ... thankfully, we have not launched," he added.

Asked if NaviSite planned to take steps to compensate customers who lost service for several days, Sinha said the migration was done to make sure customers were migrated to a better platform so that their Web site would have better performance and scalability.

"In fact, the customers that are already up -- we are getting some feedback that they are seeing the difference, that it is working better," he said. "Right now, our focus is on making sure all our customers' [Web sites] are back up and all issues are resolved, and we can get them back into their businesses. Then obviously to keep our customers, we want to make sure they are happy and they do business with us, so we would do whatever is possible and whatever is right and appropriate. But we just have not addressed those issues yet."

Sinha also said NaviSite, a publicly traded company, has not yet determined the cost of the failed migration.

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