MESQUITE, Texas (CBS HOUSTON) – A North Texas woman has been arrested after being accused of posting Facebook photos of an undercover policeman who testified against her friend in court.

Mesquite police arrested Melissa Walthall, 30, for allegedly posting the photo of the officer, who authorities say recently testified in a drug case against her friend. Her Facebook post identified the person as an undercover officer, according to a federal affidavit.

After a caller tipped off Mesquite police to Walthall’s Facebook post about a week ago, an investigator found that it posed a “viable threat to that officer’s safety,” the affidavit said.

The Dallas Morning News reports that her friend, George Pickens, 34, was upset about the officer’s testimony and found his photograph on Facebook while researching him online.

Pickens’ brother, Bobby Stedham, used the photo to make fliers, and the two men planned to display them like garage sale signs, according to the affidavit. Police reported finding them while searching Pickens’ Dallas-area house.

Stedham, 26, has been charged with retaliation, and Pickens faces federal drug and weapons charges, based on items police reported finding during the search of his house, the Houston Chronicle reported.

Mitch Landry, the deputy executive director of the Texas Municipal Police Association in Austin, said his organization has discussed with its members the perils of social media — particularly for those involved in undercover work.

“Our best advice is — if you don’t want that information out there, don’t have those accounts,” Landry told the newspaper. “There’s no way to be truly anonymous if you have a Facebook page.”

Many police departments have not yet developed social media policies and guidelines for their officers. The Dallas County Sheriff’s Department, for example, has an electronic etiquette policy that prohibits such things as vulgar language or sending obscene messages. It does not address the use of social media.

Lt. Bill Hedgpeth, Mesquite police’s spokesman, said his department does not have a set policy but periodically reminds officers to check their social media privacy settings so they allow only friends to view personal information on Facebook.

“The Internet can be a dangerous place,” Hedgpeth told the Chronicle, who added that he got rid of his Facebook account.