By Daniel Roberts, reporter

Next week brings more than one American tradition: Thanksgiving turkey followed by a rush of frenzied bargain-hunters at the malls on Black Friday.

Unfortunately for some retailers, the Internet has added a new layer to the tradition: their ads posted and scrutinized earlier than stores intended, thanks to web sites that reveal them ahead of time.

Already this year, major names in holiday shopping—including Target (TGT), Kohl’s (KSS), Best Buy (BBY), Wal-Mart (WMT), and Staples (SPLS)—have watched helplessly as many of their ads have been posted on web sites such as bfinside.com and bfads.net. Some promotions appeared as early as October.

Most consumers assume that the companies leak their own ads intentionally to drum up early excitement for their sales, but that’s not always the case. A handful of retailers, including Home Depot (HD) and Wal-Mart, make a point to send letters threatening legal action against those who have posted Black Friday ads without permission.

“Black Friday would not be Black Friday without these threatening letters each year,” says Dev Shapiro of the site Gottadeal.com, which has been posting 2010 ads from some of the biggest brands for weeks now.

Even though the letters have become routine from some corporations, Shapiro said he still takes them half-seriously, and he doesn’t believe that stores typically leak their own ads.

Some big retailers send out preemptive warnings, before any ad has been posted. Home Depot, Shapiro says, sent a “very strongly-worded email” in September demanding that Gottadeal.com refrain from posting an ad which Shapiro said he’d had in possession for a month when he received the email.

Wal-Mart, meanwhile, sent a snail mail letter insisting that posting the ads without permission would violate intellectual property, reveal trade secrets, and seriously damage its business. Wal-Mart did not respond to requests for comment by publication time.

So how do these sites obtain the ads before they’re ready for prime time? They come from anonymous sources, employees inside of the companies, or sometimes the companies themselves. Wal-Mart sends some sites the official ads on the condition they hold off until a certain date, a move that can backfire. “It’s very difficult to withhold information anymore,” says John Bell, a board member at Word of Mouth Marketing Association. “You can’t really embargo anything.”

The authenticity of the submissions is often difficult to prove. Sometimes an ad shows up in an email that “literally looks like someone stole it off a manager’s desk, took it to the bathroom and took a photo, and sent it to us,” according to Shapiro. He’s also had to translate the contents of a Spanish ad for Wal-Mart, and he’s received anonymous submissions that turned out to be four years old.

Shapiro admits he may post inaccurate or incomplete ads. He plainly tells users not to “take them as gospel.”

Corporate marketing response

Some businesses fight back, in whatever ways they can. For example, Best Buy will no longer allow shoppers to bring in an already-purchased item on Black Friday and get it price-adjusted to the sale price. Otherwise, shoppers could conceivably see the ads online early and buy ahead of the rush, then come back to get the sale price.

Others, like Staples and Lowe’s, try to beat the sites by using Facebook and Twitter to post their ads early, figuring that if sites are going to post them anyway, they may as well ensure that what’s out there is accurate.

Home Depot spokesperson Jean Niemi insists that they do care about their discounts being released early. “It doesn’t help us to have them out early,” she says. “There are more than a hundred different versions of our ad, based on local market pricing and product availability. So the last thing we would want is for someone to come in and be disappointed that we don’t have the discount they saw online.”

Niemi adds that Home Depot does not release its ads until midnight on Wednesday, so that they’re in the newspaper circulars, and online, on Thanksgiving. In addition, if shoppers go to the store’s web site they can enter their zip code and see the ad tailored to their particular area, which would certainly prevent the problems that can result from seeing a leaked ad meant for a different region.

Drew Panayiotou, CMO of Best Buy, echoes these sentiments. “Best Buy has never intentionally leaked its Black Friday circular in advance,” he says. “We are encouraging everyone to log onto BestBuy.com this Sunday evening, November 21, for the official Black Friday circular with stellar deals on the hottest products.”

But there’s no need to wait. Thanks to the ads being up on these sites already, we can report that some of Best Buy’s stellar deals may include: $150 off any Samsung laptop; the Verizon Fascinate Android phone for $9 (after rebates); $20 off Belkin wireless routers; and assorted DVDs, including The Hangover and The Blind Side, for $3.99.