Plurk published some examples of the "rip-off" code.
Microsoft has indefinitely suspended its Chinese microblogging service MSN Juku after admitting that it "copied" code used to create the site.
A vendor contracted to work for the software giant was caught lifting code from a rival Canadian start-up, Plurk.
According to Plurk as much as 80% of the basecode was "stolen directly".
Microsoft apologised to Plurk, saying "we are obviously very disappointed but we assume responsibility for this situation".
Microsoft China launched Juku in November.
Bloggers and Taiwanese users of rival service Plurk first alerted the Canadian firm to the fact that a large amount of the base code appeared to have been stolen.
Plurk responded: "We were shocked and outraged when we saw with our own eyes the cosmetic similarities Microsoft's new offering had with Plurk....Microsoft China's offering ripped off our service."
It was not just the look and feel of the site, that was the same.
"On closer inspection we found that much of the codebase and data structures... are identical snapshots of our code. That it is Microsoft doing the copying in broad daylight makes it even more incredulous," Plurk said.
Microsoft was quick to issue an apology.
"The vendor has now acknowledged that a portion of the code they provided was indeed copied," it said in a statement.
"We are a company that respects intellectual property and it was never our intent to have a site that was not respectful of the work that others in the industry have done," it said.
"We will be reaching out to them [Plurk] directly to explain what happened and the steps we have taken to resolve the situation," it added.