WASHINGTON (Reuters) --

When Google Inc.'s 19 million daily users look up a long-lost classmate, send e-mail or bounce around the Web more quickly with its new Web Accelerator, records of that activity don't go away.

In an era of increased government surveillance, privacy watchdogs worry that Google's vast archive of Internet activity could prove a tempting target for abuse.

Like many other online businesses, Google tracks how its search engine and other services are used, and who uses them. Unlike many other businesses, Google holds onto that information for years.

Some privacy experts who otherwise give Google high marks say the company's records could become a handy data bank for government investigators who rely on business records to circumvent Watergate-era laws that limit their own ability to track U.S. residents.

At a time when libraries delete lending records as soon as a book is returned, Google should purge its records after a certain point to protect users, they say.