More than 100 people suspected of having spied for the now defunct East German State Security Service have been arrested this year, a spokesman for the Federal Criminal Police Office says.

The number is three times higher than last year's figure.Most of the investigations were based on tips by ex-STASI officers who, in defiance of instructions from their former bosses, put themselves at the service of their one-time adversaries.

The defectors wanted to prove their loyalty to the new united German state and to be either granted freedom from prosecution or leniency, the spokesman said.

The number of arrests was said to be an inaccurate reflection of the amount of spying that actually took place, however. Suspected spies who had been regarded as "top agents" several years ago were interrogated and released because it was impossible for them to flee the country.

The extent of STASI espionage directed at what was once West Germany has surprised even experienced counterintelligence officials.

It was particularly painful for them to expose first-rate moles sitting in the Office for the Protection of the Constitution, the Military Counterintelligence Service and the Federal Intelligence Service.

The presence of those spies showed that the effectiveness of West German counterintelligence was evidently quite limited, the spokesman said.

According to police officials, most of the STASI's sniffing was aimed at the classic target: defense institutions. Most of the damage was done by office workers, clerks and computer specialists, not high-ranking officials.

The spies managed to copy or electronically divert an unbelievable amount of confidential information. NATO and the arms industry were also heavily targeted.