However, both American Science and ICx are still way up from their share prices on Dec. 24. American Science was trading at $71 on the day before Christmas. ICx was trading at $4.98 on Christmas Eve. Implant Sciences, albeit a tiny stock, has received a lot of play among anti-terror investors, but ended the day down more than 1.4%, to 34 and a half cents. Implant Sciences also saw its heaviest trading on Monday, when it shed almost half of its meager value. OSI Systems ( OSIS) was the other big anti-terror winner on Friday, ending up close to 10%, or a gain of $2.75, to $31.64. Unlike the other security technology stocks, which experienced heavy selling earlier in the week and recovered on Thursday and Friday, OSI shares saw their best trading on the last day of the week. OSI shares were traded at volume above 3 million on Friday, versus an average of 656,000 shares traded. Three times as many OSI shares were traded on Friday as on any other day during 2010's first week. OSI also attained a 52-week high during Friday's session, but closed 79 cents below that Friday high level of $32.43. -- Reported by Eric Rosenbaum in New York.