SAN FRANCISCO  Just days after the T-Mobile G1 smartphone went on the market, a group of security researchers have found what they call a serious flaw in the Android software from Google that runs it.

One of the researchers, Charles A. Miller, notified Google of the flaw this week and said he was publicizing it now because he believed that cellphone users were not generally aware that increasingly sophisticated smartphones faced the same threats that plague Internet-connected personal computers.

Mr. Miller, a former National Security Agency computer security specialist, said the flaw could be exploited by an attacker who might trick a G1 user into visiting a booby-trapped Web site.

The G1  the so-called Google phone  went on sale at T-Mobile stores on Wednesday.

Google executives acknowledged the issue but said that the security features of the phone would limit the extent of damage that could be done by an intruder, compared with today’s PCs and other cellphones.