From the news today:

A man charged with trying to kill a Danish cartoonist was arrested last year in an alleged plot to harm U.S. Secretary of State Hillary Clinton, officials said. […] The suspect was one of four people arrested last summer in Nairobi in an alleged plot to harm Clinton during her tour of African countries, the newspaper Politken reported. The suspect was released from a Kenyan jail in September because of a lack of evidence and returned to Denmark, where he had been living, Sky News reported Sunday.

Just a few days ago, CNN reported:

That announcement led to questions about how many other former Guantanamo detainees may be planning to carry out terrorist attacks.

Pentagon officials have not released updated statistics on recidivism, but the unclassified report from April says 74 individuals, or 14 percent of former detainees, have turned to or are suspected of having turned to terrorism activity since their release.

Of the more than 530 detainees released from the prison between 2002 and last spring, 27 were confirmed to have engaged in terrorist activities and 47 were suspected of participating in a terrorist act, according to Pentagon statistics cited in the spring report.

More at Wikisource.

These are actually lower than the general population, where about 65% of prisoners are expected to be rearrested within 3 years. The numbers seem lower in recent years, about 58%. More at Wikipedia.