1. The introduction of data of one security security category into data of a lower security classification or different security category. . 2. Relative to numbering guidelines and FCC regulations, contamination occurs when at least one telephone number within a thousands-block of telephone numbers is not available for assignment to end users or customers. Blocks contaminated up to and including 10 percent are eligible for donation. For purposes of this provision, a telephone number is "not available for assignment" if it is classified as administrative, aging, assigned, intermediate, or reserved as defined in FCC rules (FCC 00-104, §52. 7 (h). )