One of the sources relaying the fact that Kritstiina Koivunen, a sociologist who works on Kurdistan, had been deported from Turkey, on the 19th of December 2006, Zaman Online published a note from Cihan News Agency.
Cihan News Agency reported that Koivunen had been "declared persona non grata by the Ministry for Internal Affairs"; it is a common way of expressing someone unwelcome, but it's direct translation - "an unacceptable person" - is quite telling.
The deportation of this unwelcome, unacceptable voice has been mentioned elsewhere - on from Holland to Kurdistan, in Helsingin Sanomat (reproduced on Kurdish Media), on Kurd Net, in Newsroom Finland (by the Ministry for Foreign Affairs of Finland) and on Rasti, amongst others (not including (notably Finnish) non-English-language sources).
I haven't been able to find any more up-to-date information, so I haven't heard the government of Turkey's excuse for the decision I posted earlier, supposedly "based on state security".
As the Turkish Daily News note that I reproduced mentioned and as Helsingin Sanomat observed, "[t]he apparent reason for the arrest and deportation was that Koivunen had violated a ban on her entering the country", but, obviously, that merely moves the same question one step back: why was she banned from entering the country, for their to be a ban to violate?
[Updated on the 1st of January 2006.]
I just found what may be Kristiina Koivunen's own blog, though I can't be sure as it's in Finnish; it does have an English-language interview she gave to Farhad M. Hassan for the Gulan Weekly, which has been reproduced there, but it doesn't say any more about why she was deported than the other sources.