The target, ContentGuard, is a leading provider of DRM technology, which controls how copyrighted digital content, such as DVDs or software, can be viewed, used, or abused.
Microsoft and Time Warner announced in April 2004 that they, together with ContentGuard, had purchased most of the stake held in that company by its original owner, Xerox.
The Commission began an investigation into the purchase in August, after an initial review gave rise to fears that the purchase of a leading DRM technology provider such as ContentGuard might put Microsoft into a dominant position in that sector.
EU competition regulators were due to rule on the matter by 6th January, but halted the review when Paris-based Thomson announced in December that it had agreed to buy a 33% voting stake in ContentGuard, potentially reducing the antitrust impact on the market.
According to the Associated Press, the Commission has now received additional information from the companies, enabling it to restart the probe.
The investigation will still focus on the initial Microsoft-Time Warner deal because Microsoft's sale of shares to Thomson took place before Microsoft's initial purchase had been approved by the Commission.
"The Commission has to assess to what extent the deal with Thomson could have taken place without the initial deal," Commission spokesman Jonathan Todd told the Associated Press.