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A recent study found that the widely-used secret questions for Web authentication can easily be guessed. The study focused on making secret questions easier to remember for the user and harder to break by others. Our approach is authentication through the use of an individual's personal and dynamic Internet activities. We hypothesize that(More)
Context. X-ray surveys of Active Galactic Nuclei (AGN) indicate " cosmic downsizing " , with the comoving number density of high-luminosity objects peaking at higher redshifts (z ∼ 2) than low-luminosity AGN (z < 1). Aims. We test whether downsizing is caused by activity shifting towards low-mass black holes accreting at near-Eddington rates, or by a change(More)
The high-frequency-peaked BL Lac (HBL) 1ES 0806+524 (z = 0.138) was discovered in VHE γ rays in 2008. Until now, the broad-band spectrum of 1ES 0806+524 has been only poorly characterized, in particular at high energies. We analysed multiwavelength observations from γ rays to radio performed from 2011 January to March, which were triggered by the high(More)