year attacks
1972 5
1973 3
1974 4
1975 5
1976 2
1977 14
1978 5
1979 2
1980 4
1981 5
1982 6
1983 6
1984 5
1985 3
1986 13
1987 9
1988 9
1989 13
1990 18
1991 18
1992 10
1993 18
1994 22
1995 19
1996 13
1997 11
1998 9
1999 15
2000 23
2001 17
2002 14
2003 6
2004 11