Hostilities between AOL and Microsoft over instant messaging continued Monday and as the row enters its second week, legal experts reckon a court battle is imminent. Microsoft confirmed this morning that users of its MSN Messenger service, which promises access to AOL's 40 million subscribers, was working with AOL's Instant Messenger. AOL UK did not know whether that facility would be blocked again -- last week AOL engineers produced blocks against MSN users -- Microsoft twice countered with patches to hurdle the blockades.. At the heart of the argument, AOL says Microsoft and Yahoo are invading its network infrastructure and such invasions threaten to open its private service up to "spam, pornography and all kinds of things people don't want". Although Microsoft did not deny its users could look for pornography in the 'profiles' of potential Messenger 'friends' Tom Bowman, sales director at MSN UK says its software has "built-in privacy protection". Tony Willoughby, a partner with the law firm Rouse and Co International Willoughby and Partners says that if the companies are not prepared to negotiate, a temporary restraining order preventing Microsoft from entering AOL's network is likely. "This is clearly a serious issue... One would imagine they [AOL] will look for a legal solution," says Willoughby. " If AOL has a 'cause of action' [a legal peg to hang a claim] such as breach of confidence or copyright infringement, an immediate injunction pending the final outcome could be issued. Effectively a temporary restraining order." But a legal battle could backfire on AOL which, according to Microsoft, was approached two years ago to work on a universal messaging standard. Microsoft says AOL officials were "not interested" giving the impression that AOL wants to keep its users in and other users out of its proprietary service. Robin Bynoe, a partner with the law firm Charles Russel and Co. agrees with Willoughby but says in the long term, AOL will be the loser. "Everyone wants open standards so that the Net is available to all and AOL seems to be resisting that. In the short term I think they [AOL] probably will look for some legal blockade of MSN's activities. I can't see what the alternative is if they're not speaking with one another." AOL was unable to respond in time for this news item.