strange serial problem

hello, i experiment strange serial data out problems...i upload a simple program to diecimila... the blink example with serial communication sending "on" and "off"...

1h later, the arduino start to send very fast strange data messages like this !!!

(...) 00u..062000.%006..00...066G00.1G0&.,00...0.&000..80&..00&.50.-001L.00-630.-%60.2006&4G06u.0.V-.0.5G056200..5054460..G0...G05.-0&..606VG0..2G03..0.5.40.5G0.6"00...0..&Z0.,80.24G0.6.0..i405..06..G06v.0...y0.6006..G01.102,V00t&00...G0.-.0v.U00v.G0.f.00.$.0..q00u.G062600.%.06.G00..G066.00.1.0&.700..G0.&.00..60&.000&.w0.-601L.60-650.-%50.2606&4.06u.0.V-60.5.0562*0..G0544G0...0....05.40&..G06V.0..2v03..0.5.80.5.0.6"00..10..&00.,60.2Xw0.6G0...G05.406.*106v00...G0.6.06..301.002&V0..000.-80v.200v..0.f000.$00.. (...)

what is this??

thanks,

alex