Google may conceal YouTube users' identities when it hands a database of their viewing habits to Viacom International in response to a court order, the companies agreed Monday.

Although Google must still disclose a database logging which videos were viewed and when, it may conceal the User ID, IP (Internet Protocol) Address and Visitor ID fields showing who watched them and where from. Instead, it will replacing them with unique values preserving the relationship between them but protecting users' anonymity, according to papers filed Monday with the U.S. District Court for the Southern District of New York.

Viacom filed suit against the search engine company and its video-sharing subsidiary in 2007, accusing them of illegally distributing its copyright content. In the discovery phase of the case, it requested information from YouTube's user database. Viacom hopes the data will show its copyright content is of more interest to YouTube's users than video created by the users themselves.

Online privacy campaigners were appalled at the judge's order to disclose the data. Among them, the Electronic Frontier Foundation warned that it "threatens to expose deeply private information about what videos are watched by YouTube users."

Monday's agreement will go some way to allaying those fears, although much will depend on the system Google uses to choose the values with which it replaces YouTube User IDs in the disclosed database.

When researchers at AOL published logs of the online searches conducted by some of the company's users in August 2006, some of those users were quickly identified despite the researchers' replacement of user names with unique, anonymous codes. AOL promised to beef up its privacy policy after that incident, which resulted in the firing of two researchers and the resignation of the company's chief technology officer.

As part of Monday's agreement, Viacom said it will "not engage in any efforts to circumvent the encryption" used to conceal the IP addresses and YouTube User IDs in the logging database.